Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
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	2,770	903
Total number of securities in an unrealized loss position equal to or greater than 12 months	574	619
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	$ 22,995	$ 10,561
Less than 12 Months Gross Unrealized Loss	688	89
Equal to or Greater than 12 Months Estimated Fair Value	4,630	5,403
Equal to or Greater than 12 Months Gross Unrealized Loss	425	260
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	9,566	1,762
Less than 12 Months Gross Unrealized Loss	321	21
Equal to or Greater than 12 Months Estimated Fair Value	1,229	1,413
Equal to or Greater than 12 Months Gross Unrealized Loss	118	68
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	2,587	4,764
Less than 12 Months Gross Unrealized Loss	61	36
Equal to or Greater than 12 Months Estimated Fair Value	1,318	1,573
Equal to or Greater than 12 Months Gross Unrealized Loss	129	80
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	3,209	2,308
Less than 12 Months Gross Unrealized Loss	95	13
Equal to or Greater than 12 Months Estimated Fair Value	1,103	1,292
Equal to or Greater than 12 Months Gross Unrealized Loss	74	41
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	2,924	636
Less than 12 Months Gross Unrealized Loss	105	8
Equal to or Greater than 12 Months Estimated Fair Value	433	559
Equal to or Greater than 12 Months Gross Unrealized Loss	71	54
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	577	171
Less than 12 Months Gross Unrealized Loss	15	3
Equal to or Greater than 12 Months Estimated Fair Value	102	106
Equal to or Greater than 12 Months Gross Unrealized Loss	8	4
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	2,897	603
Less than 12 Months Gross Unrealized Loss	66	6
Equal to or Greater than 12 Months Estimated Fair Value	344	335
Equal to or Greater than 12 Months Gross Unrealized Loss	20	10
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	735	165
Less than 12 Months Gross Unrealized Loss	4	0
Equal to or Greater than 12 Months Estimated Fair Value	33	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 and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	500	152
Less than 12 Months Gross Unrealized Loss	21	2
Equal to or Greater than 12 Months Estimated Fair Value	68	50
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 4	$ 1