Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 11,350	$ 25,234
Gross Unrealized Losses, Less than 12 Months	506	2,946
Estimated Fair Value, 12 Months or Longer	18,262	4,277
Gross Unrealized Losses, 12 Months or Longer	3,280	1,110
Estimated Fair Value, Total	29,612	29,511
Gross Unrealized Losses, Total	3,786	4,056
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	7,681	15,946
Gross Unrealized Losses, Less than 12 Months	350	1,585
Estimated Fair Value, 12 Months or Longer	10,087	1,634
Gross Unrealized Losses, 12 Months or Longer	1,559	424
Estimated Fair Value, Total	17,768	17,580
Gross Unrealized Losses, Total	1,909	2,009
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,486	4,079
Gross Unrealized Losses, Less than 12 Months	64	769
Estimated Fair Value, 12 Months or Longer	2,783	456
Gross Unrealized Losses, 12 Months or Longer	729	170
Estimated Fair Value, Total	4,269	4,535
Gross Unrealized Losses, Total	793	939
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,886	4,660
Gross Unrealized Losses, Less than 12 Months	82	565
Estimated Fair Value, 12 Months or Longer	4,963	2,093
Gross Unrealized Losses, 12 Months or Longer	949	498
Estimated Fair Value, Total	6,849	6,753
Gross Unrealized Losses, Total	1,031	1,063
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	822	1,406
Gross Unrealized Losses, Less than 12 Months	35	144
Estimated Fair Value, 12 Months or Longer	1,810	1,143
Gross Unrealized Losses, 12 Months or Longer	409	303
Estimated Fair Value, Total	2,632	2,549
Gross Unrealized Losses, Total	444	447
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	325	1,167
Gross Unrealized Losses, Less than 12 Months	15	159
Estimated Fair Value, 12 Months or Longer	1,171	408
Gross Unrealized Losses, 12 Months or Longer	242	96
Estimated Fair Value, Total	1,496	1,575
Gross Unrealized Losses, Total	257	255
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	739	2,087
Gross Unrealized Losses, Less than 12 Months	32	262
Estimated Fair Value, 12 Months or Longer	1,982	542
Gross Unrealized Losses, 12 Months or Longer	298	99
Estimated Fair Value, Total	2,721	2,629
Gross Unrealized Losses, Total	330	361
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	84	76
Gross Unrealized Losses, Less than 12 Months	2	1
Estimated Fair Value, 12 Months or Longer	34	16
Gross Unrealized Losses, 12 Months or Longer	1	1
Estimated Fair Value, Total	118	92
Gross Unrealized Losses, Total	3	2
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	213	473
Gross Unrealized Losses, Less than 12 Months	8	26
Estimated Fair Value, 12 Months or Longer	395	78
Gross Unrealized Losses, 12 Months or Longer	42	17
Estimated Fair Value, Total	608	551
Gross Unrealized Losses, Total	$ 50	$ 43