Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 890	$ 8,543
Gross Unrealized Losses, Less than 12 Months	26	340
Estimated Fair Value, 12 Months or Longer	200	825
Gross Unrealized Losses, 12 Months or Longer	16	55
Estimated Fair Value, Total	1,090	9,368
Gross Unrealized Losses, Total	42	395
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	20	517
Gross Unrealized Losses, Less than 12 Months	0	8
Estimated Fair Value, 12 Months or Longer	2	5
Gross Unrealized Losses, 12 Months or Longer	0	1
Estimated Fair Value, Total	22	522
Gross Unrealized Losses, Total	0	9
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	150	1,932
Gross Unrealized Losses, Less than 12 Months	0	23
Estimated Fair Value, 12 Months or Longer	38	1,119
Gross Unrealized Losses, 12 Months or Longer	1	34
Estimated Fair Value, Total	188	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	83	728
Gross Unrealized Losses, Less than 12 Months	2	10
Estimated Fair Value, 12 Months or Longer	26	397
Gross Unrealized Losses, 12 Months or Longer	1	22
Estimated Fair Value, Total	109	1,125
Gross Unrealized Losses, Total	3	32
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	416	834
Gross Unrealized Losses, Less than 12 Months	3	21
Estimated Fair Value, 12 Months or Longer	6	125
Gross Unrealized Losses, 12 Months or Longer	1	3
Estimated Fair Value, Total	422	959
Gross Unrealized Losses, Total	4	24
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	649	3,494
Gross Unrealized Losses, Less than 12 Months	5	54
Estimated Fair Value, 12 Months or Longer	70	1,641
Gross Unrealized Losses, 12 Months or Longer	3	59
Estimated Fair Value, Total	719	5,135
Gross Unrealized Losses, Total	8	113
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	14	21
Gross Unrealized Losses, Less than 12 Months	0	0
Estimated Fair Value, 12 Months or Longer	4	19
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	18	40
Gross Unrealized Losses, Total	0	0
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	17	114
Gross Unrealized Losses, Less than 12 Months	0	2
Estimated Fair Value, 12 Months or Longer	2	124
Gross Unrealized Losses, 12 Months or Longer	0	2
Estimated Fair Value, Total	19	238
Gross Unrealized Losses, Total	0	4
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,590	12,689
Gross Unrealized Losses, Less than 12 Months	31	404
Estimated Fair Value, 12 Months or Longer	278	2,614
Gross Unrealized Losses, 12 Months or Longer	19	117
Estimated Fair Value, Total	1,868	15,303
Gross Unrealized Losses, Total	$ 50	$ 521

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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