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Investments - Reconciliation of Available-for-Sale Securities from Cost Basis to Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 90,371		$ 88,978
Gross Unrealized Gains	1,143		754
Gross Unrealized Losses	6,231		7,786
Allowance for Credit Losses	97	$ 85	46	$ 47	$ 39	$ 19
Fair Value	85,186		81,900
Corporate bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	68,127		67,991
Gross Unrealized Gains	867		560
Gross Unrealized Losses	5,479		6,704
Allowance for Credit Losses	49	36	14	17	13	8
Fair Value	63,466		61,833
U.S. government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	641		427
Gross Unrealized Gains	8		3
Gross Unrealized Losses	31		40
Allowance for Credit Losses	0		0
Fair Value	618		390
State and municipal bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,190		2,391
Gross Unrealized Gains	39		27
Gross Unrealized Losses	230		270
Allowance for Credit Losses	0		0
Fair Value	1,999		2,148
Foreign government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	276		277
Gross Unrealized Gains	14		12
Gross Unrealized Losses	50		56
Allowance for Credit Losses	0		0
Fair Value	240		233
RMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,040		1,849
Gross Unrealized Gains	40		23
Gross Unrealized Losses	114		162
Allowance for Credit Losses	6	5	7	6	6	6
Fair Value	1,960		1,703
CMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,141		1,713
Gross Unrealized Gains	16		5
Gross Unrealized Losses	93		135
Allowance for Credit Losses	0		0
Fair Value	2,064		1,583
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,728		14,103
Gross Unrealized Gains	135		99
Gross Unrealized Losses	227		409
Allowance for Credit Losses	41	$ 43	24	$ 23	$ 19	$ 4
Fair Value	14,595		13,769
Hybrid and redeemable preferred securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	228		227
Gross Unrealized Gains	24		25
Gross Unrealized Losses	7		10
Allowance for Credit Losses	1		1
Fair Value	$ 244		$ 241