Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 3,967	$ 2,148
Gross Unrealized Losses, Less than 12 Months	263	31
Estimated Fair Value, 12 Months or Longer	105	272
Gross Unrealized Losses, 12 Months or Longer	9	14
Estimated Fair Value, Total	4,072	2,420
Gross Unrealized Losses, Total	272	45
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	2,095	914
Gross Unrealized Losses, Less than 12 Months	137	21
Estimated Fair Value, 12 Months or Longer	56	186
Gross Unrealized Losses, 12 Months or Longer	6	11
Estimated Fair Value, Total	2,151	1,100
Gross Unrealized Losses, Total	143	32
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	94	34
Gross Unrealized Losses, Less than 12 Months	1	0
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	94	34
Gross Unrealized Losses, Total	1
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	53	249
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	21	30
Gross Unrealized Losses, 12 Months or Longer	1	0
Estimated Fair Value, Total	74	279
Gross Unrealized Losses, Total	2	1
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	971	381
Gross Unrealized Losses, Less than 12 Months	92	3
Estimated Fair Value, 12 Months or Longer	14	20
Gross Unrealized Losses, 12 Months or Longer	1	2
Estimated Fair Value, Total	985	401
Gross Unrealized Losses, Total	93	5
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	746	449
Gross Unrealized Losses, Less than 12 Months	32	3
Estimated Fair Value, 12 Months or Longer	14	33
Gross Unrealized Losses, 12 Months or Longer	1	1
Estimated Fair Value, Total	760	482
Gross Unrealized Losses, Total	33	4
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,770	1,079
Gross Unrealized Losses, Less than 12 Months	125	7
Estimated Fair Value, 12 Months or Longer	49	83
Gross Unrealized Losses, 12 Months or Longer	3	3
Estimated Fair Value, Total	1,819	1,162
Gross Unrealized Losses, Total	128	10
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	4	62
Gross Unrealized Losses, Less than 12 Months	0	2
Estimated Fair Value, 12 Months or Longer	0	2
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	4	64
Gross Unrealized Losses, Total	0	2
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	4	59
Gross Unrealized Losses, Less than 12 Months	0	1
Estimated Fair Value, 12 Months or Longer	0	1
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	4	60
Gross Unrealized Losses, Total	$ 0	$ 1