Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 5,085	$ 1,666
Gross Unrealized Losses, Less than 12 Months	158	74
Estimated Fair Value, 12 Months or Longer	476	64
Gross Unrealized Losses, 12 Months or Longer	24	3
Estimated Fair Value, Total	5,561	1,730
Gross Unrealized Losses, Total	182	77
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,868	609
Gross Unrealized Losses, Less than 12 Months	66	21
Estimated Fair Value, 12 Months or Longer	82	12
Gross Unrealized Losses, 12 Months or Longer	5	1
Estimated Fair Value, Total	1,950	621
Gross Unrealized Losses, Total	71	22
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	866	33
Gross Unrealized Losses, Less than 12 Months	31	0
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	866	33
Gross Unrealized Losses, Total	31
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	1,584	71
Gross Unrealized Losses, Less than 12 Months	40	1
Estimated Fair Value, 12 Months or Longer	12	11
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	1,596	82
Gross Unrealized Losses, Total	40	1
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	320	533
Gross Unrealized Losses, Less than 12 Months	9	40
Estimated Fair Value, 12 Months or Longer	285	28
Gross Unrealized Losses, 12 Months or Longer	15	2
Estimated Fair Value, Total	605	561
Gross Unrealized Losses, Total	24	42
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	337	344
Gross Unrealized Losses, Less than 12 Months	3	9
Estimated Fair Value, 12 Months or Longer	97	13
Gross Unrealized Losses, 12 Months or Longer	4	0
Estimated Fair Value, Total	434	357
Gross Unrealized Losses, Total	7	9
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	2,241	948
Gross Unrealized Losses, Less than 12 Months	52	50
Estimated Fair Value, 12 Months or Longer	394	52
Gross Unrealized Losses, 12 Months or Longer	19	2
Estimated Fair Value, Total	2,635	1,000
Gross Unrealized Losses, Total	71	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	7	3
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	65	63
Gross Unrealized Losses, Total	7	3
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	45	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	45	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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