Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 2,148	$ 12,689
Gross Unrealized Losses, Less than 12 Months	31	404
Estimated Fair Value, 12 Months or Longer	272	2,614
Gross Unrealized Losses, 12 Months or Longer	14	117
Estimated Fair Value, Total	2,420	15,303
Gross Unrealized Losses, Total	45	521
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	914	8,543
Gross Unrealized Losses, Less than 12 Months	21	340
Estimated Fair Value, 12 Months or Longer	186	825
Gross Unrealized Losses, 12 Months or Longer	11	55
Estimated Fair Value, Total	1,100	9,368
Gross Unrealized Losses, Total	32	395
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	34	517
Gross Unrealized Losses, Less than 12 Months	0	8
Estimated Fair Value, 12 Months or Longer	0	5
Gross Unrealized Losses, 12 Months or Longer	0	1
Estimated Fair Value, Total	34	522
Gross Unrealized Losses, Total		9
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	249	1,932
Gross Unrealized Losses, Less than 12 Months	1	23
Estimated Fair Value, 12 Months or Longer	30	1,119
Gross Unrealized Losses, 12 Months or Longer	0	34
Estimated Fair Value, Total	279	3,051
Gross Unrealized Losses, Total	1	57
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	381	728
Gross Unrealized Losses, Less than 12 Months	3	10
Estimated Fair Value, 12 Months or Longer	20	397
Gross Unrealized Losses, 12 Months or Longer	2	22
Estimated Fair Value, Total	401	1,125
Gross Unrealized Losses, Total	5	32
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	449	834
Gross Unrealized Losses, Less than 12 Months	3	21
Estimated Fair Value, 12 Months or Longer	33	125
Gross Unrealized Losses, 12 Months or Longer	1	3
Estimated Fair Value, Total	482	959
Gross Unrealized Losses, Total	4	24
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,079	3,494
Gross Unrealized Losses, Less than 12 Months	7	54
Estimated Fair Value, 12 Months or Longer	83	1,641
Gross Unrealized Losses, 12 Months or Longer	3	59
Estimated Fair Value, Total	1,162	5,135
Gross Unrealized Losses, Total	10	113
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	62	21
Gross Unrealized Losses, Less than 12 Months	2	0
Estimated Fair Value, 12 Months or Longer	2	19
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	64	40
Gross Unrealized Losses, Total	2	0
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	59	114
Gross Unrealized Losses, Less than 12 Months	1	2
Estimated Fair Value, 12 Months or Longer	1	124
Gross Unrealized Losses, 12 Months or Longer	0	2
Estimated Fair Value, Total	60	238
Gross Unrealized Losses, Total	$ 1	$ 4

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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