Investments - Current and Long-Term Fixed Maturity Securities, Available-For-Sale (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 30,701	$ 31,336
Gross Unrealized Gains	313	496
Gross Unrealized Losses	(1,261)	(1,338)
Allowance For Credit Losses	(4)	(4)
Estimated Fair Value	29,749	30,490
United States Government securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	1,794	1,873
Gross Unrealized Gains	4	25
Gross Unrealized Losses	(85)	(54)
Allowance For Credit Losses	0	0
Estimated Fair Value	1,713	1,844
Government sponsored securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	129	112
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(5)	(3)
Allowance For Credit Losses	0	0
Estimated Fair Value	125	110
Foreign government securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	71	5
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(2)	(2)
Allowance For Credit Losses	0	0
Estimated Fair Value	69	4
States, municipalities and political subdivisions, tax-exempt
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	3,626	3,985
Gross Unrealized Gains	45	69
Gross Unrealized Losses	(152)	(152)
Allowance For Credit Losses	0	0
Estimated Fair Value	3,519	3,902
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	15,953	14,838
Gross Unrealized Gains	203	322
Gross Unrealized Losses	(526)	(580)
Allowance For Credit Losses	(2)	(2)
Estimated Fair Value	15,628	14,578
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	4,140	4,071
Gross Unrealized Gains	24	40
Gross Unrealized Losses	(304)	(279)
Allowance For Credit Losses	0	0
Estimated Fair Value	3,860	3,832
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	1,976	2,174
Gross Unrealized Gains	9	13
Gross Unrealized Losses	(91)	(138)
Allowance For Credit Losses	(2)	(2)
Estimated Fair Value	1,892	2,047
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	3,012	4,278
Gross Unrealized Gains	27	25
Gross Unrealized Losses	(96)	(130)
Allowance For Credit Losses	0	0
Estimated Fair Value	$ 2,943	$ 4,173

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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