Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
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	1,018	1,711
Total number of securities in an unrealized loss position equal to or greater than 12 months	362	475
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	$ 11,201	$ 17,060
Less than 12 Months Gross Unrealized Loss	195	671
Equal to or Greater than 12 Months Estimated Fair Value	2,428	2,757
Equal to or Greater than 12 Months Gross Unrealized Loss	184	251
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	2,285	4,632
Less than 12 Months Gross Unrealized Loss	52	187
Equal to or Greater than 12 Months Estimated Fair Value	726	699
Equal to or Greater than 12 Months Gross Unrealized Loss	47	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	5,006	4,396
Less than 12 Months Gross Unrealized Loss	71	237
Equal to or Greater than 12 Months Estimated Fair Value	529	0
Equal to or Greater than 12 Months Gross Unrealized Loss	56	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	2,152	3,457
Less than 12 Months Gross Unrealized Loss	42	107
Equal to or Greater than 12 Months Estimated Fair Value	383	818
Equal to or Greater than 12 Months Gross Unrealized Loss	13	32
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	540	1,443
Less than 12 Months Gross Unrealized Loss	12	64
Equal to or Greater than 12 Months Estimated Fair Value	547	573
Equal to or Greater than 12 Months Gross Unrealized Loss	59	104
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	300	887
Less than 12 Months Gross Unrealized Loss	6	35
Equal to or Greater than 12 Months Estimated Fair Value	43	29
Equal to or Greater than 12 Months Gross Unrealized Loss	3	3
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	667	1,553
Less than 12 Months Gross Unrealized Loss	10	26
Equal to or Greater than 12 Months Estimated Fair Value	93	171
Equal to or Greater than 12 Months Gross Unrealized Loss	4	5
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	120	450
Less than 12 Months Gross Unrealized Loss	0	5
Equal to or Greater than 12 Months Estimated Fair Value	97	461
Equal to or Greater than 12 Months Gross Unrealized Loss	2	8
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	131	242
Less than 12 Months Gross Unrealized Loss	2	10
Equal to or Greater than 12 Months Estimated Fair Value	10	6
Equal to or Greater than 12 Months Gross Unrealized Loss	0	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	1	57
Less than 12 Months Gross Unrealized Loss	0	2
Equal to or Greater than 12 Months Estimated Fair Value	16	40
Equal to or Greater than 12 Months Gross Unrealized Loss	1	7
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	0	57
Less than 12 Months Gross Unrealized Loss	0	2
Equal to or Greater than 12 Months Estimated Fair Value	16	40
Equal to or Greater than 12 Months Gross Unrealized Loss	1	7
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	1	0
Less than 12 Months Gross Unrealized Loss	0	0
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 0	$ 0