Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 776	$ 8,543
Gross Unrealized Losses, Less than 12 Months	22	340
Estimated Fair Value, 12 Months or Longer	498	825
Gross Unrealized Losses, 12 Months or Longer	22	55
Estimated Fair Value, Total	1,274	9,368
Gross Unrealized Losses, Total	44	395
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	19	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	21	522
Gross Unrealized Losses, Total	0	9
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	163	1,932
Gross Unrealized Losses, Less than 12 Months	0	23
Estimated Fair Value, 12 Months or Longer	134	1,119
Gross Unrealized Losses, 12 Months or Longer	2	34
Estimated Fair Value, Total	297	3,051
Gross Unrealized Losses, Total	2	57
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	58	728
Gross Unrealized Losses, Less than 12 Months	2	10
Estimated Fair Value, 12 Months or Longer	69	397
Gross Unrealized Losses, 12 Months or Longer	2	22
Estimated Fair Value, Total	127	1,125
Gross Unrealized Losses, Total	4	32
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	386	834
Gross Unrealized Losses, Less than 12 Months	5	21
Estimated Fair Value, 12 Months or Longer	77	125
Gross Unrealized Losses, 12 Months or Longer	2	3
Estimated Fair Value, Total	463	959
Gross Unrealized Losses, Total	7	24
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	607	3,494
Gross Unrealized Losses, Less than 12 Months	7	54
Estimated Fair Value, 12 Months or Longer	280	1,641
Gross Unrealized Losses, 12 Months or Longer	6	59
Estimated Fair Value, Total	887	5,135
Gross Unrealized Losses, Total	13	113
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	0	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	4	40
Gross Unrealized Losses, Total	0	0
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	3	114
Gross Unrealized Losses, Less than 12 Months	0	2
Estimated Fair Value, 12 Months or Longer	11	124
Gross Unrealized Losses, 12 Months or Longer	0	2
Estimated Fair Value, Total	14	238
Gross Unrealized Losses, Total	0	4
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,405	12,689
Gross Unrealized Losses, Less than 12 Months	29	404
Estimated Fair Value, 12 Months or Longer	795	2,614
Gross Unrealized Losses, 12 Months or Longer	28	117
Estimated Fair Value, Total	2,200	15,303
Gross Unrealized Losses, Total	$ 57	$ 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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