Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 3,483	$ 25,234
Gross Unrealized Losses, Less than 12 Months	74	2,946
Estimated Fair Value, 12 Months or Longer	22,248	4,277
Gross Unrealized Losses, 12 Months or Longer	2,921	1,110
Estimated Fair Value, Total	25,731	29,511
Gross Unrealized Losses, Total	2,995	4,056
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,943	15,946
Gross Unrealized Losses, Less than 12 Months	37	1,585
Estimated Fair Value, 12 Months or Longer	13,406	1,634
Gross Unrealized Losses, 12 Months or Longer	1,308	424
Estimated Fair Value, Total	15,349	17,580
Gross Unrealized Losses, Total	1,345	2,009
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	598	4,079
Gross Unrealized Losses, Less than 12 Months	18	769
Estimated Fair Value, 12 Months or Longer	3,104	456
Gross Unrealized Losses, 12 Months or Longer	685	170
Estimated Fair Value, Total	3,702	4,535
Gross Unrealized Losses, Total	703	939
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	233	1,406
Gross Unrealized Losses, Less than 12 Months	4	144
Estimated Fair Value, 12 Months or Longer	2,212	1,143
Gross Unrealized Losses, 12 Months or Longer	421	303
Estimated Fair Value, Total	2,445	2,549
Gross Unrealized Losses, Total	425	447
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	200	1,167
Gross Unrealized Losses, Less than 12 Months	5	159
Estimated Fair Value, 12 Months or Longer	1,184	408
Gross Unrealized Losses, 12 Months or Longer	225	96
Estimated Fair Value, Total	1,384	1,575
Gross Unrealized Losses, Total	230	255
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	392	2,087
Gross Unrealized Losses, Less than 12 Months	8	262
Estimated Fair Value, 12 Months or Longer	1,869	542
Gross Unrealized Losses, 12 Months or Longer	248	99
Estimated Fair Value, Total	2,261	2,629
Gross Unrealized Losses, Total	256	361
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	825	4,660
Gross Unrealized Losses, Less than 12 Months	17	565
Estimated Fair Value, 12 Months or Longer	5,265	2,093
Gross Unrealized Losses, 12 Months or Longer	894	498
Estimated Fair Value, Total	6,090	6,753
Gross Unrealized Losses, Total	911	1,063
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	65	76
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	23	16
Gross Unrealized Losses, 12 Months or Longer	1	1
Estimated Fair Value, Total	88	92
Gross Unrealized Losses, Total	2	2
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	52	473
Gross Unrealized Losses, Less than 12 Months	1	26
Estimated Fair Value, 12 Months or Longer	450	78
Gross Unrealized Losses, 12 Months or Longer	33	17
Estimated Fair Value, Total	502	551
Gross Unrealized Losses, Total	$ 34	$ 43