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	3,249	3,580
Total number of securities in an unrealized loss position equal to or greater than 12 months	1,638	1,307
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	$ 50,486	$ 51,095
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	923	2,243
Equal to or Greater than 12 Months Estimated Fair Value	14,631	14,238
Equal to or Greater than 12 Months Gross Unrealized Loss	1,143	1,696
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	6,647	11,471
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	161	466
Equal to or Greater than 12 Months Estimated Fair Value	3,015	2,938
Equal to or Greater than 12 Months Gross Unrealized Loss	232	298
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	19,305	9,104
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	275	523
Equal to or Greater than 12 Months Estimated Fair Value	362	141
Equal to or Greater than 12 Months Gross Unrealized Loss	28	20
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	6,856	5,955
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	202	260
Equal to or Greater than 12 Months Estimated Fair Value	1,669	918
Equal to or Greater than 12 Months Gross Unrealized Loss	113	113
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	5,856	10,147
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	149	573
Equal to or Greater than 12 Months Estimated Fair Value	6,137	5,493
Equal to or Greater than 12 Months Gross Unrealized Loss	601	998
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	7,731	9,449
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	106	291
Equal to or Greater than 12 Months Estimated Fair Value	2,025	1,800
Equal to or Greater than 12 Months Gross Unrealized Loss	86	109
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	560	1,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	13	80
Equal to or Greater than 12 Months Estimated Fair Value	165	56
Equal to or Greater than 12 Months Gross Unrealized Loss	11	6
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,976	2,224
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	28
Equal to or Greater than 12 Months Estimated Fair Value	921	2,328
Equal to or Greater than 12 Months Gross Unrealized Loss	40	103
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,555	998
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12	22
Equal to or Greater than 12 Months Estimated Fair Value	337	564
Equal to or Greater than 12 Months Gross Unrealized Loss	32	49
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	133	244
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	20
Equal to or Greater than 12 Months Estimated Fair Value	86	136
Equal to or Greater than 12 Months Gross Unrealized Loss	5	33
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	133	105
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	13
Equal to or Greater than 12 Months Estimated Fair Value	4	11
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
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	139
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	7
Equal to or Greater than 12 Months Estimated Fair Value	82	125
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 5	$ 33