Reinsurance - Reinsurance Recoverables (Details) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	$ 4,131
Allowance for uncollectible reinsurance, including assets held for sale	(35)
Market risk benefits	951	$ 1,301
Total reinsurance recoverables, including assets held for sale	5,047
Held-for-Sale \| Medicare Advantage and related Cigna Healthcare businesses
Ceded Credit Risk [Line Items]
Reinsurance recoverable classified as assets of businesses held for sale	209
Other Current Assets
Ceded Credit Risk [Line Items]
Reinsurance recoverables	166
Berkshire Hathway Life Insurance Company Of Nebraska and Other Recoverables
Ceded Credit Risk [Line Items]
Market risk benefits	951
Fair value of collateral contractually required to meet or exceed carrying value of recoverable
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	663
Collateral provisions exist that may mitigate risk of credit loss
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	2,989
No collateral
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	479
Ongoing Operations
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	485
Ongoing Operations \| A- equivalent and higher current ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	85
Ongoing Operations \| BBB- to BBB+ equivalent current credit ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	60
Ongoing Operations \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	340
Ongoing Operations \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	145
Ongoing Operations \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| A- equivalent and higher current ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Ongoing Operations \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB- to BBB+ equivalent current credit ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Ongoing Operations \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	145
Ongoing Operations \| Collateral provisions exist that may mitigate risk of credit loss
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	7
Ongoing Operations \| Collateral provisions exist that may mitigate risk of credit loss \| A- equivalent and higher current ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Ongoing Operations \| Collateral provisions exist that may mitigate risk of credit loss \| BBB- to BBB+ equivalent current credit ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Ongoing Operations \| Collateral provisions exist that may mitigate risk of credit loss \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	7
Ongoing Operations \| No collateral
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	333
Ongoing Operations \| No collateral \| A- equivalent and higher current ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	85
Ongoing Operations \| No collateral \| BBB- to BBB+ equivalent current credit ratings
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	60
Ongoing Operations \| No collateral \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	188
Acquisition, disposition or run-off activities
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	3,646
Acquisition, disposition or run-off activities \| BBB+ equivalent and higher current ratings \| Lincoln National Life and Lincoln Life & Annuity of New York
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	2,619
Acquisition, disposition or run-off activities \| BBB+ equivalent and higher current ratings \| Empower Annuity Insurance Company
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	128
Acquisition, disposition or run-off activities \| BBB+ equivalent and higher current ratings \| Prudential Insurance Company of America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	351
Acquisition, disposition or run-off activities \| BBB+ equivalent and higher current ratings \| Life Insurance Company of North America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	334
Acquisition, disposition or run-off activities \| BBB+ equivalent and higher current ratings \| Other
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	204
Acquisition, disposition or run-off activities \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	10
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	518
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB+ equivalent and higher current ratings \| Lincoln National Life and Lincoln Life & Annuity of New York
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB+ equivalent and higher current ratings \| Empower Annuity Insurance Company
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB+ equivalent and higher current ratings \| Prudential Insurance Company of America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	351
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB+ equivalent and higher current ratings \| Life Insurance Company of North America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| BBB+ equivalent and higher current ratings \| Other
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	167
Acquisition, disposition or run-off activities \| Fair value of collateral contractually required to meet or exceed carrying value of recoverable \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	2,982
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| BBB+ equivalent and higher current ratings \| Lincoln National Life and Lincoln Life & Annuity of New York
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	2,619
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| BBB+ equivalent and higher current ratings \| Empower Annuity Insurance Company
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| BBB+ equivalent and higher current ratings \| Prudential Insurance Company of America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| BBB+ equivalent and higher current ratings \| Life Insurance Company of North America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	334
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| BBB+ equivalent and higher current ratings \| Other
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	23
Acquisition, disposition or run-off activities \| Collateral provisions exist that may mitigate risk of credit loss \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	6
Acquisition, disposition or run-off activities \| No collateral
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	146
Acquisition, disposition or run-off activities \| No collateral \| BBB+ equivalent and higher current ratings \| Lincoln National Life and Lincoln Life & Annuity of New York
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| No collateral \| BBB+ equivalent and higher current ratings \| Empower Annuity Insurance Company
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	128
Acquisition, disposition or run-off activities \| No collateral \| BBB+ equivalent and higher current ratings \| Prudential Insurance Company of America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| No collateral \| BBB+ equivalent and higher current ratings \| Life Insurance Company of North America
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	0
Acquisition, disposition or run-off activities \| No collateral \| BBB+ equivalent and higher current ratings \| Other
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	14
Acquisition, disposition or run-off activities \| No collateral \| Not rated
Ceded Credit Risk [Line Items]
Reinsurance recoverables before market risk benefits, including assets held for sale	$ 4