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Investments - Reconciliation of Available-for-Sale Securities from Cost Basis to Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 88,998		$ 88,231
Gross Unrealized Gains	1,378		1,054
Gross Unrealized Losses	5,758		6,966
Allowance for Credit Losses	47	$ 39	19	$ 21	$ 25	$ 21
Fair Value	84,571		82,300
Corporate bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	68,637		68,811
Gross Unrealized Gains	1,064		820
Gross Unrealized Losses	4,927		5,757
Allowance for Credit Losses	17	13	8	9	13	9
Fair Value	64,757		63,866
U.S. government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	415		414
Gross Unrealized Gains	8		7
Gross Unrealized Losses	25		28
Allowance for Credit Losses	0		0
Fair Value	398		393
State and municipal bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,427		2,675
Gross Unrealized Gains	87		97
Gross Unrealized Losses	196		230
Allowance for Credit Losses	0		0
Fair Value	2,318		2,542
Foreign government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	278		309
Gross Unrealized Gains	16		15
Gross Unrealized Losses	46		46
Allowance for Credit Losses	0		0
Fair Value	248		278
RMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,789		1,719
Gross Unrealized Gains	38		27
Gross Unrealized Losses	107		138
Allowance for Credit Losses	6	6	6	6	6	7
Fair Value	1,714		1,602
CMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,661		1,520
Gross Unrealized Gains	14		5
Gross Unrealized Losses	116		181
Allowance for Credit Losses	0		0
Fair Value	1,559		1,344
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	13,557		12,556
Gross Unrealized Gains	125		62
Gross Unrealized Losses	331		571
Allowance for Credit Losses	23	$ 19	4	$ 5	$ 5	$ 4
Fair Value	13,328		12,043
Hybrid and redeemable preferred securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	234		227
Gross Unrealized Gains	26		21
Gross Unrealized Losses	10		15
Allowance for Credit Losses	1		1
Fair Value	$ 249		$ 232