Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 9,836	$ 25,234
Gross Unrealized Losses, Less than 12 Months	605	2,946
Estimated Fair Value, 12 Months or Longer	21,281	4,277
Gross Unrealized Losses, 12 Months or Longer	4,283	1,110
Estimated Fair Value, Total	31,117	29,511
Gross Unrealized Losses, Total	4,888	4,056
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	6,374	15,946
Gross Unrealized Losses, Less than 12 Months	378	1,585
Estimated Fair Value, 12 Months or Longer	12,794	1,634
Gross Unrealized Losses, 12 Months or Longer	2,059	424
Estimated Fair Value, Total	19,168	17,580
Gross Unrealized Losses, Total	2,437	2,009
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,593	4,079
Gross Unrealized Losses, Less than 12 Months	138	769
Estimated Fair Value, 12 Months or Longer	2,902	456
Gross Unrealized Losses, 12 Months or Longer	1,014	170
Estimated Fair Value, Total	4,495	4,535
Gross Unrealized Losses, Total	1,152	939
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,562	4,660
Gross Unrealized Losses, Less than 12 Months	79	565
Estimated Fair Value, 12 Months or Longer	5,128	2,093
Gross Unrealized Losses, 12 Months or Longer	1,162	498
Estimated Fair Value, Total	6,690	6,753
Gross Unrealized Losses, Total	1,241	1,063
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	680	1,406
Gross Unrealized Losses, Less than 12 Months	30	144
Estimated Fair Value, 12 Months or Longer	2,094	1,143
Gross Unrealized Losses, 12 Months or Longer	569	303
Estimated Fair Value, Total	2,774	2,549
Gross Unrealized Losses, Total	599	447
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	273	1,167
Gross Unrealized Losses, Less than 12 Months	9	159
Estimated Fair Value, 12 Months or Longer	1,161	408
Gross Unrealized Losses, 12 Months or Longer	267	96
Estimated Fair Value, Total	1,434	1,575
Gross Unrealized Losses, Total	276	255
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	609	2,087
Gross Unrealized Losses, Less than 12 Months	40	262
Estimated Fair Value, 12 Months or Longer	1,873	542
Gross Unrealized Losses, 12 Months or Longer	326	99
Estimated Fair Value, Total	2,482	2,629
Gross Unrealized Losses, Total	366	361
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	106	76
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	21	16
Gross Unrealized Losses, 12 Months or Longer	1	1
Estimated Fair Value, Total	127	92
Gross Unrealized Losses, Total	2	2
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	201	473
Gross Unrealized Losses, Less than 12 Months	9	26
Estimated Fair Value, 12 Months or Longer	436	78
Gross Unrealized Losses, 12 Months or Longer	47	17
Estimated Fair Value, Total	637	551
Gross Unrealized Losses, Total	$ 56	$ 43