Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed maturity securities - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	$ 6,175	$ 3,979
Gross Unrealized Losses - Less than 12 months	322	84
Estimated Fair Value - 12 months or greater	738	1,238
Gross Unrealized Losses - 12 months or greater	48	26
Estimated Fair Value	6,913	5,217
Gross Unrealized Losses	370	110
Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	806	220
Gross Unrealized Losses - Less than 12 months	120	38
Estimated Fair Value - 12 months or greater	77	110
Gross Unrealized Losses - 12 months or greater	14	8
Estimated Fair Value	883	330
Gross Unrealized Losses	134	46
Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	5,369	3,759
Gross Unrealized Losses - Less than 12 months	202	46
Estimated Fair Value - 12 months or greater	661	1,128
Gross Unrealized Losses - 12 months or greater	34	18
Estimated Fair Value	6,030	4,887
Gross Unrealized Losses	236	64
Corporate Debt Securities [Member] | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	672	220
Gross Unrealized Losses - Less than 12 months	94	38
Estimated Fair Value - 12 months or greater	60	100
Gross Unrealized Losses - 12 months or greater	9	7
Estimated Fair Value	732	320
Gross Unrealized Losses	103	45
Corporate Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	2,446	1,936
Gross Unrealized Losses - Less than 12 months	108	29
Estimated Fair Value - 12 months or greater	83	293
Gross Unrealized Losses - 12 months or greater	10	7
Estimated Fair Value	2,529	2,229
Gross Unrealized Losses	118	36
Residential mortgage-backed securities | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	225	367
Gross Unrealized Losses - Less than 12 months	1	2
Estimated Fair Value - 12 months or greater	0	84
Gross Unrealized Losses - 12 months or greater	0	1
Estimated Fair Value	225	451
Gross Unrealized Losses	1	3
Asset-backed securities | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	19	0
Gross Unrealized Losses - Less than 12 months	14	0
Estimated Fair Value - 12 months or greater	4	0
Gross Unrealized Losses - 12 months or greater	1	0
Estimated Fair Value	23	0
Gross Unrealized Losses	15	0
Asset-backed securities | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	1,304	773
Gross Unrealized Losses - Less than 12 months	37	5
Estimated Fair Value - 12 months or greater	552	739
Gross Unrealized Losses - 12 months or greater	20	9
Estimated Fair Value	1,856	1,512
Gross Unrealized Losses	57	14
Commercial mortgage-backed securities | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	22	0
Gross Unrealized Losses - Less than 12 months	3	0
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	22	0
Gross Unrealized Losses	3	0
Commercial mortgage-backed securities | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	355	253
Gross Unrealized Losses - Less than 12 months	19	3
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	355	253
Gross Unrealized Losses	19	3
US Government Agencies Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	0	49
Gross Unrealized Losses - Less than 12 months	0	1
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	0	49
Gross Unrealized Losses	0	1
US States and Political Subdivisions Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	84	103
Gross Unrealized Losses - Less than 12 months	2	2
Estimated Fair Value - 12 months or greater	15	12
Gross Unrealized Losses - 12 months or greater	2	1
Estimated Fair Value	99	115
Gross Unrealized Losses	4	3
Debt Security, Government, Non-US [Member] | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	93	0
Gross Unrealized Losses - Less than 12 months	9	0
Estimated Fair Value - 12 months or greater	13	10
Gross Unrealized Losses - 12 months or greater	4	1
Estimated Fair Value	106	10
Gross Unrealized Losses	13	1
Debt Security, Government, Non-US [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	955	278
Gross Unrealized Losses - Less than 12 months	35	4
Estimated Fair Value - 12 months or greater	11	0
Gross Unrealized Losses - 12 months or greater	2	0
Estimated Fair Value	966	278
Gross Unrealized Losses	$ 37	$ 4