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Investments - Reconciliation of Available-for-Sale Securities from Cost Basis to Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 88,371		$ 88,231
Gross Unrealized Gains	728		1,054
Gross Unrealized Losses	8,023		6,966
Allowance for Credit Losses	39	$ 21	19	$ 25	$ 37	$ 21
Fair Value	81,037		82,300
Corporate bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	68,308		68,811
Gross Unrealized Gains	547		820
Gross Unrealized Losses	6,819		5,757
Allowance for Credit Losses	13	10	8	13	26	9
Fair Value	62,023		63,866
U.S. government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	422		414
Gross Unrealized Gains	3		7
Gross Unrealized Losses	37		28
Allowance for Credit Losses	0		0
Fair Value	388		393
State and municipal bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,449		2,675
Gross Unrealized Gains	45		97
Gross Unrealized Losses	254		230
Allowance for Credit Losses	0		0
Fair Value	2,240		2,542
Foreign government bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	298		309
Gross Unrealized Gains	12		15
Gross Unrealized Losses	54		46
Allowance for Credit Losses	0		0
Fair Value	256		278
RMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,696		1,719
Gross Unrealized Gains	20		27
Gross Unrealized Losses	156		138
Allowance for Credit Losses	6	6	6	6	6	7
Fair Value	1,554		1,602
CMBS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,556		1,520
Gross Unrealized Gains	4		5
Gross Unrealized Losses	158		181
Allowance for Credit Losses	0		0
Fair Value	1,402		1,344
ABS
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	13,424		12,556
Gross Unrealized Gains	75		62
Gross Unrealized Losses	533		571
Allowance for Credit Losses	19	$ 4	4	$ 5	$ 4	$ 4
Fair Value	12,947		12,043
Hybrid and redeemable preferred securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	218		227
Gross Unrealized Gains	22		21
Gross Unrealized Losses	12		15
Allowance for Credit Losses	1		1
Fair Value	$ 227		$ 232