Investments - AFS - Unrealized Gains and Losses (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,631	$ 5,280
Gross Unrealized Gains	37	27
Non-Credit Related Losses	(344)	(401)
Allowance for Credit Losses	0	0	$ (17)	$ (16)
Fair Value	5,324	4,906
U.S. government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	581	426
Gross Unrealized Gains	2	1
Non-Credit Related Losses	(16)	(20)
Allowance for Credit Losses	0	0
Fair Value	567	407
U.K. government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	42	32
Gross Unrealized Gains	0	0
Non-Credit Related Losses	(3)	(3)
Allowance for Credit Losses	0	0
Fair Value	39	29
Other government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	293	292
Gross Unrealized Gains	1	0
Non-Credit Related Losses	(21)	(24)
Allowance for Credit Losses	0	0
Fair Value	273	268
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,785	2,602
Gross Unrealized Gains	15	7
Non-Credit Related Losses	(231)	(266)
Allowance for Credit Losses	0	0	(16)	(15)
Fair Value	2,569	2,343
Municipal
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	89	94
Gross Unrealized Gains	0	0
Non-Credit Related Losses	(13)	(15)
Allowance for Credit Losses	0	0
Fair Value	76	79
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	438	409
Gross Unrealized Gains	3	2
Non-Credit Related Losses	(32)	(38)
Allowance for Credit Losses	0	0
Fair Value	409	373
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	665	711
Gross Unrealized Gains	4	4
Non-Credit Related Losses	(26)	(33)
Allowance for Credit Losses	0	0	$ (1)	$ (1)
Fair Value	643	682
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	738	714
Gross Unrealized Gains	12	13
Non-Credit Related Losses	(2)	(2)
Allowance for Credit Losses	0	0
Fair Value	$ 748	$ 725

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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-Topic 320
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-Paragraph 2
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Amount, before tax, of unrealized loss 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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