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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	$ 98,632		$ 97,415
Gross Unrealized Gains	1,116		747
Gross Unrealized Losses	8,971		11,005
Allowance for Credit Losses	97	$ 85	46	$ 48	$ 39	$ 19
Fair Value	90,680		87,111
Corporate bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	75,526		75,556
Gross Unrealized Gains	862		563
Gross Unrealized Losses	7,988		9,655
Allowance for Credit Losses	49	36	14	17	13	8
Fair Value	68,351		66,450
U.S. government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	642		429
Gross Unrealized Gains	8		3
Gross Unrealized Losses	31		41
Allowance for Credit Losses	0		0
Fair Value	619		391
State and municipal bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,605		2,798
Gross Unrealized Gains	21		18
Gross Unrealized Losses	391		445
Allowance for Credit Losses	0		0
Fair Value	2,235		2,371
Foreign government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	281		282
Gross Unrealized Gains	14		11
Gross Unrealized Losses	51		56
Allowance for Credit Losses	0		0
Fair Value	244		237
RMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,246		2,066
Gross Unrealized Gains	39		24
Gross Unrealized Losses	161		220
Allowance for Credit Losses	6	5	7	7	6	6
Fair Value	2,118		1,863
CMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,244		1,817
Gross Unrealized Gains	13		4
Gross Unrealized Losses	107		156
Allowance for Credit Losses	0		0
Fair Value	2,150		1,665
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,846		14,226
Gross Unrealized Gains	135		99
Gross Unrealized Losses	234		421
Allowance for Credit Losses	41	$ 43	24	$ 23	$ 19	$ 4
Fair Value	14,706		13,880
Hybrid and redeemable preferred securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	242		241
Gross Unrealized Gains	24		25
Gross Unrealized Losses	8		11
Allowance for Credit Losses	1		1
Fair Value	$ 257		$ 254