Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
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	1,388	1,850
Total number of securities in an unrealized loss position equal to or greater than 12 months	468	394
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	$ 13,462	$ 18,228
Less than 12 Months Gross Unrealized Loss	519	570
Equal to or Greater than 12 Months Estimated Fair Value	2,626	1,934
Equal to or Greater than 12 Months Gross Unrealized Loss	235	264
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	3,525	4,569
Less than 12 Months Gross Unrealized Loss	145	278
Equal to or Greater than 12 Months Estimated Fair Value	625	571
Equal to or Greater than 12 Months Gross Unrealized Loss	90	115
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	1,231	1,650
Less than 12 Months Gross Unrealized Loss	60	96
Equal to or Greater than 12 Months Estimated Fair Value	532	605
Equal to or Greater than 12 Months Gross Unrealized Loss	98	98
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	3,548	4,037
Less than 12 Months Gross Unrealized Loss	188	53
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	2,642	4,305
Less than 12 Months Gross Unrealized Loss	69	73
Equal to or Greater than 12 Months Estimated Fair Value	811	495
Equal to or Greater than 12 Months Gross Unrealized Loss	32	41
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	548	373
Less than 12 Months Gross Unrealized Loss	21	12
Equal to or Greater than 12 Months Estimated Fair Value	29	19
Equal to or Greater than 12 Months Gross Unrealized Loss	3	2
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	433	1,818
Less than 12 Months Gross Unrealized Loss	4	28
Equal to or Greater than 12 Months Estimated Fair Value	461	194
Equal to or Greater than 12 Months Gross Unrealized Loss	8	6
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,307	1,346
Less than 12 Months Gross Unrealized Loss	22	21
Equal to or Greater than 12 Months Estimated Fair Value	164	44
Equal to or Greater than 12 Months Gross Unrealized Loss	3	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	228	130
Less than 12 Months Gross Unrealized Loss	10	9
Equal to or Greater than 12 Months Estimated Fair Value	4	6
Equal to or Greater than 12 Months Gross Unrealized Loss	1	1
Equity securities
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	57	31
Less than 12 Months Gross Unrealized Loss	2	6
Equal to or Greater than 12 Months Estimated Fair Value	40	41
Equal to or Greater than 12 Months Gross Unrealized Loss	7	8
Non-redeemable preferred stock
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	57	25
Less than 12 Months Gross Unrealized Loss	2	1
Equal to or Greater than 12 Months Estimated Fair Value	40	40
Equal to or Greater than 12 Months Gross Unrealized Loss	7	8
Common stock
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	0	6
Less than 12 Months Gross Unrealized Loss	0	5
Equal to or Greater than 12 Months Estimated Fair Value	0	1
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 0	$ 0