Significant Accounting Policies - Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred acquisition costs, beginning of the period	$ 1,502	$ 1,219
Capitalizations	544	548
Amortization expense	(299)	(265)
Deferred acquisition costs, end of the period	$ 1,747	$ 1,502

Amount of amortization expense (reversal of expense) for deferred policy acquisition costs.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480016/944-40-65-2

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-2B

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479401/944-30-55-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479868/944-20-45-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(7)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479432/944-30-50-1

Name:	us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration