Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Mar. 31, 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	5,111	2,598
Total number of securities in an unrealized loss position equal to or greater than 12 months	1,887	1,955
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	$ 70,303	$ 41,943
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,586	435
Equal to or Greater than 12 Months Estimated Fair Value	21,980	23,375
Equal to or Greater than 12 Months Gross Unrealized Loss	1,847	1,468
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	20,465	5,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	642	92
Equal to or Greater than 12 Months Estimated Fair Value	4,426	4,115
Equal to or Greater than 12 Months Gross Unrealized Loss	415	259
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	19,105	18,273
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	224	93
Equal to or Greater than 12 Months Estimated Fair Value	3,378	3,560
Equal to or Greater than 12 Months Gross Unrealized Loss	333	186
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	4,510	4,234
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	137	83
Equal to or Greater than 12 Months Estimated Fair Value	3,297	3,251
Equal to or Greater than 12 Months Gross Unrealized Loss	260	229
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	8,932	4,422
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	259	99
Equal to or Greater than 12 Months Estimated Fair Value	5,835	6,802
Equal to or Greater than 12 Months Gross Unrealized Loss	538	577
RMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	10,855	6,359
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	237	50
Equal to or Greater than 12 Months Estimated Fair Value	3,713	4,159
Equal to or Greater than 12 Months Gross Unrealized Loss	209	141
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	774	182
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	24	2
Equal to or Greater than 12 Months Estimated Fair Value	302	346
Equal to or Greater than 12 Months Gross Unrealized Loss	19	12
ABS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	2,593	1,695
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	15	7
Equal to or Greater than 12 Months Estimated Fair Value	551	729
Equal to or Greater than 12 Months Gross Unrealized Loss	27	31
CMBS
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	3,069	1,174
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	48	9
Equal to or Greater than 12 Months Estimated Fair Value	478	413
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 46	$ 33