Investments (Continuous Gross Unrealized Losses for Fixed Maturity Securities AFS by Sector) (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Total number of securities in an unrealized loss position less than 12 months	1,160	2,988
Total number of securities in an unrealized loss position equal to or greater than 12 months	1,235	1,022
Fixed maturity securities
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	$ 6,535	$ 20,812
Less than 12 Months Gross Unrealized Loss	188	797
Equal to or Greater than 12 Months Estimated Fair Value	9,660	8,118
Equal to or Greater than 12 Months Gross Unrealized Loss	335	552
U.S. corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	2,647	10,450
Less than 12 Months Gross Unrealized Loss	85	465
Equal to or Greater than 12 Months Estimated Fair Value	3,743	2,290
Equal to or Greater than 12 Months Gross Unrealized Loss	146	194
U.S. government and agency
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	109	359
Less than 12 Months Gross Unrealized Loss	1	7
Equal to or Greater than 12 Months Estimated Fair Value	852	1,355
Equal to or Greater than 12 Months Gross Unrealized Loss	28	103
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	747	1,550
Less than 12 Months Gross Unrealized Loss	3	21
Equal to or Greater than 12 Months Estimated Fair Value	2,609	2,567
Equal to or Greater than 12 Months Gross Unrealized Loss	56	99
Foreign corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,574	3,916
Less than 12 Months Gross Unrealized Loss	64	199
Equal to or Greater than 12 Months Estimated Fair Value	1,113	746
Equal to or Greater than 12 Months Gross Unrealized Loss	83	107
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	310	2,264
Less than 12 Months Gross Unrealized Loss	16	52
Equal to or Greater than 12 Months Estimated Fair Value	1,024	800
Equal to or Greater than 12 Months Gross Unrealized Loss	17	34
State and political subdivision
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	31	346
Less than 12 Months Gross Unrealized Loss	1	7
Equal to or Greater than 12 Months Estimated Fair Value	129	158
Equal to or Greater than 12 Months Gross Unrealized Loss	2	8
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	860	1,407
Less than 12 Months Gross Unrealized Loss	10	21
Equal to or Greater than 12 Months Estimated Fair Value	161	70
Equal to or Greater than 12 Months Gross Unrealized Loss	2	1
Foreign government
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	257	520
Less than 12 Months Gross Unrealized Loss	8	25
Equal to or Greater than 12 Months Estimated Fair Value	29	132
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 1	$ 6