Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 42,989		$ 42,414
Gross Unrealized Gains	705		1,022
Gross Unrealized Losses	3,278		2,995
Allowance for Credit Losses	17	$ 20	16	$ 22	$ 2	$ 1
Estimated Fair Value	40,399		40,425
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities trading	4		0
Total fixed maturity securities trading	4		0
Debt securities, amortized cost	42,993		42,414
Total fixed maturity securities	40,403		40,425
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	25,463		25,020
Gross Unrealized Gains	401		597
Gross Unrealized Losses	1,496		1,345
Allowance for Credit Losses	0	3	4	13	1	0
Estimated Fair Value	24,368		24,268
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	25,269		25,132
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	7,560		7,713
Gross Unrealized Gains	269		382
Gross Unrealized Losses	800		703
Allowance for Credit Losses	0		0
Estimated Fair Value	7,029		7,392
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	7,029		7,392
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,602		3,411
Gross Unrealized Gains	8		16
Gross Unrealized Losses	495		425
Allowance for Credit Losses	0		0
Estimated Fair Value	3,115		3,002
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,798		1,862
Gross Unrealized Gains	7		7
Gross Unrealized Losses	186		230
Allowance for Credit Losses	8		8
Estimated Fair Value	1,611		1,631
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,631		3,515
Gross Unrealized Gains	17		13
Gross Unrealized Losses	260		256
Allowance for Credit Losses	9		4
Estimated Fair Value	3,379		3,268
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,031		8,788
Gross Unrealized Gains	32		36
Gross Unrealized Losses	941		911
Allowance for Credit Losses	17	$ 17	12	$ 9	$ 1	$ 1
Estimated Fair Value	8,105		7,901
Debt Securities, Trading, Unrealized Gain (Loss) [Abstract]
Total fixed maturity securities	8,105		7,901
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	193		152
Gross Unrealized Gains	1		1
Gross Unrealized Losses	3		2
Allowance for Credit Losses	0		0
Estimated Fair Value	191		151
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	742		741
Gross Unrealized Gains	2		6
Gross Unrealized Losses	38		34
Allowance for Credit Losses	0		0
Estimated Fair Value	$ 706		$ 713