Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Total number of securities in an unrealized loss position less than 12 months	2,988	903
Total number of securities in an unrealized loss position equal to or greater than 12 months	1,022	619
Fixed maturity securities
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	$ 20,812	$ 10,561
Less than 12 Months Gross Unrealized Loss	797	89
Equal to or Greater than 12 Months Estimated Fair Value	8,118	5,403
Equal to or Greater than 12 Months Gross Unrealized Loss	552	260
U.S. corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	10,450	1,762
Less than 12 Months Gross Unrealized Loss	465	21
Equal to or Greater than 12 Months Estimated Fair Value	2,290	1,413
Equal to or Greater than 12 Months Gross Unrealized Loss	194	68
U.S. government and agency
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	359	4,764
Less than 12 Months Gross Unrealized Loss	7	36
Equal to or Greater than 12 Months Estimated Fair Value	1,355	1,573
Equal to or Greater than 12 Months Gross Unrealized Loss	103	80
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	1,550	2,308
Less than 12 Months Gross Unrealized Loss	21	13
Equal to or Greater than 12 Months Estimated Fair Value	2,567	1,292
Equal to or Greater than 12 Months Gross Unrealized Loss	99	41
Foreign corporate
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	3,916	636
Less than 12 Months Gross Unrealized Loss	199	8
Equal to or Greater than 12 Months Estimated Fair Value	746	559
Equal to or Greater than 12 Months Gross Unrealized Loss	107	54
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	2,264	603
Less than 12 Months Gross Unrealized Loss	52	6
Equal to or Greater than 12 Months Estimated Fair Value	800	335
Equal to or Greater than 12 Months Gross Unrealized Loss	34	10
State and political subdivision
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	346	171
Less than 12 Months Gross Unrealized Loss	7	3
Equal to or Greater than 12 Months Estimated Fair Value	158	106
Equal to or Greater than 12 Months Gross Unrealized Loss	8	4
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	1,407	165
Less than 12 Months Gross Unrealized Loss	21	0
Equal to or Greater than 12 Months Estimated Fair Value	70	75
Equal to or Greater than 12 Months Gross Unrealized Loss	1	2
Foreign government
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity Available for sale [Abstract]
Less than 12 months Estimated Fair Value	520	152
Less than 12 Months Gross Unrealized Loss	25	2
Equal to or Greater than 12 Months Estimated Fair Value	132	50
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 6	$ 1