Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed Maturities [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 3,979	$ 12,040
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	84	408
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,238	7,216
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	26	340
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	5,217	19,256
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	110	748
External Credit Rating, Investment Grade [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	3,759	11,155
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	46	359
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,128	7,093
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	18	325
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,887	18,248
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	64	684
External Credit Rating, Investment Grade [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,936	8,505
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	29	302
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	293	3,612
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	7	195
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,229	12,117
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	36	497
External Credit Rating, Investment Grade [Member] | Canadian Provincial Governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	132
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	0	132
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	0	2
External Credit Rating, Investment Grade [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	367	270
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	2	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	84	836
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1	23
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	451	1,106
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3	25
External Credit Rating, Investment Grade [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	773	1,102
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	5	24
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	739	382
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	9	9
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,512	1,484
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	14	33
External Credit Rating, Investment Grade [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	253	384
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	3	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	415
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	14
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	253	799
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3	18
External Credit Rating, Investment Grade [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	49	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	1,086
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	58
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	49	1,086
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	1	58
External Credit Rating, Investment Grade [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	103	104
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	2	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	12	157
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1	7
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	115	261
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3	9
External Credit Rating, Investment Grade [Member] | Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	278	790
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	4	25
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	473
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	17
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	278	1,263
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	4	42
External Credit Rating, Non Investment Grade [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	220	885
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	38	49
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	110	123
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	8	15
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	330	1,008
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	46	64
External Credit Rating, Non Investment Grade [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	220	756
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	38	43
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	100	123
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	7	15
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	320	879
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	45	58
External Credit Rating, Non Investment Grade [Member] | Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	129
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	10	129
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 1	$ 6