Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 4,927	$ 1,666
Gross Unrealized Losses, Less than 12 Months	71	74
Estimated Fair Value, 12 Months or Longer	341	64
Gross Unrealized Losses, 12 Months or Longer	18	3
Estimated Fair Value, Total	5,268	1,730
Gross Unrealized Losses, Total	89	77
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,853	609
Gross Unrealized Losses, Less than 12 Months	37	21
Estimated Fair Value, 12 Months or Longer	88	12
Gross Unrealized Losses, 12 Months or Longer	5	1
Estimated Fair Value, Total	1,941	621
Gross Unrealized Losses, Total	42	22
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	885	33
Gross Unrealized Losses, Less than 12 Months	15	0
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	885	33
Gross Unrealized Losses, Total	15
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,295	71
Gross Unrealized Losses, Less than 12 Months	6	1
Estimated Fair Value, 12 Months or Longer	0	11
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	1,295	82
Gross Unrealized Losses, Total	6	1
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	317	533
Gross Unrealized Losses, Less than 12 Months	4	40
Estimated Fair Value, 12 Months or Longer	194	28
Gross Unrealized Losses, 12 Months or Longer	12	2
Estimated Fair Value, Total	511	561
Gross Unrealized Losses, Total	16	42
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	439	344
Gross Unrealized Losses, Less than 12 Months	3	9
Estimated Fair Value, 12 Months or Longer	58	13
Gross Unrealized Losses, 12 Months or Longer	1	0
Estimated Fair Value, Total	497	357
Gross Unrealized Losses, Total	4	9
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	2,051	948
Gross Unrealized Losses, Less than 12 Months	13	50
Estimated Fair Value, 12 Months or Longer	252	52
Gross Unrealized Losses, 12 Months or Longer	13	2
Estimated Fair Value, Total	2,303	1,000
Gross Unrealized Losses, Total	26	52
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	65	63
Gross Unrealized Losses, Less than 12 Months	4	3
Estimated Fair Value, 12 Months or Longer	1	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	66	63
Gross Unrealized Losses, Total	4	3
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	73	13
Gross Unrealized Losses, Less than 12 Months	2	0
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	73	13
Gross Unrealized Losses, Total	$ 2	$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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