Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed maturity securities - USD ($) $ in Millions	Jun. 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	$ 6,532	$ 3,979
Gross Unrealized Losses - Less than 12 months	397	84
Estimated Fair Value - 12 months or greater	743	1,238
Gross Unrealized Losses - 12 months or greater	51	26
Estimated Fair Value	7,275	5,217
Gross Unrealized Losses	448	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	926	220
Gross Unrealized Losses - Less than 12 months	130	38
Estimated Fair Value - 12 months or greater	65	110
Gross Unrealized Losses - 12 months or greater	9	8
Estimated Fair Value	991	330
Gross Unrealized Losses	139	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	5,606	3,759
Gross Unrealized Losses - Less than 12 months	267	46
Estimated Fair Value - 12 months or greater	678	1,128
Gross Unrealized Losses - 12 months or greater	42	18
Estimated Fair Value	6,284	4,887
Gross Unrealized Losses	309	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	780	220
Gross Unrealized Losses - Less than 12 months	114	38
Estimated Fair Value - 12 months or greater	53	100
Gross Unrealized Losses - 12 months or greater	6	7
Estimated Fair Value	833	320
Gross Unrealized Losses	120	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	2,359	1,936
Gross Unrealized Losses - Less than 12 months	125	29
Estimated Fair Value - 12 months or greater	67	293
Gross Unrealized Losses - 12 months or greater	9	7
Estimated Fair Value	2,426	2,229
Gross Unrealized Losses	134	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	0	367
Gross Unrealized Losses - Less than 12 months	0	2
Estimated Fair Value - 12 months or greater	28	84
Gross Unrealized Losses - 12 months or greater	1	1
Estimated Fair Value	28	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	20	0
Gross Unrealized Losses - Less than 12 months	5	0
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	20	0
Gross Unrealized Losses	5	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	1,425	773
Gross Unrealized Losses - Less than 12 months	53	5
Estimated Fair Value - 12 months or greater	558	739
Gross Unrealized Losses - 12 months or greater	29	9
Estimated Fair Value	1,983	1,512
Gross Unrealized Losses	82	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	23	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	23	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	690	253
Gross Unrealized Losses - Less than 12 months	37	3
Estimated Fair Value - 12 months or greater	13	0
Gross Unrealized Losses - 12 months or greater	1	0
Estimated Fair Value	703	253
Gross Unrealized Losses	38	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	59	103
Gross Unrealized Losses - Less than 12 months	5	2
Estimated Fair Value - 12 months or greater	12	12
Gross Unrealized Losses - 12 months or greater	2	1
Estimated Fair Value	71	115
Gross Unrealized Losses	7	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	103	0
Gross Unrealized Losses - Less than 12 months	8	0
Estimated Fair Value - 12 months or greater	12	10
Gross Unrealized Losses - 12 months or greater	3	1
Estimated Fair Value	115	10
Gross Unrealized Losses	11	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	1,073	278
Gross Unrealized Losses - Less than 12 months	47	4
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	1,073	278
Gross Unrealized Losses	$ 47	$ 4