Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) $ in Millions	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items]
Total number of securities in an unrealized loss position less than 12 months	6,572	2,598
Total number of securities in an unrealized loss position equal to or greater than 12 months	1,881	1,955
Fixed Maturity Securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	$ 88,901	$ 41,943
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,914	435
Equal to or Greater than 12 Months Estimated Fair Value	19,865	23,375
Equal to or Greater than 12 Months Gross Unrealized Loss	1,884	1,468
U.S. corporate
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	29,888	5,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,145	92
Equal to or Greater than 12 Months Estimated Fair Value	4,227	4,115
Equal to or Greater than 12 Months Gross Unrealized Loss	444	259
U.S. government and agency
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	18,165	18,273
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	217	93
Equal to or Greater than 12 Months Estimated Fair Value	3,300	3,560
Equal to or Greater than 12 Months Gross Unrealized Loss	326	186
Foreign government
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	5,007	4,234
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	258	83
Equal to or Greater than 12 Months Estimated Fair Value	2,960	3,251
Equal to or Greater than 12 Months Gross Unrealized Loss	248	229
Foreign corporate
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	14,309	4,422
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	865	99
Equal to or Greater than 12 Months Estimated Fair Value	4,676	6,802
Equal to or Greater than 12 Months Gross Unrealized Loss	568	577
RMBS
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	11,604	6,359
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	307	50
Equal to or Greater than 12 Months Estimated Fair Value	3,537	4,159
Equal to or Greater than 12 Months Gross Unrealized Loss	214	141
State and political subdivision
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	1,064	182
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	31	2
Equal to or Greater than 12 Months Estimated Fair Value	299	346
Equal to or Greater than 12 Months Gross Unrealized Loss	21	12
ABS
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	4,588	1,695
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	17	7
Equal to or Greater than 12 Months Estimated Fair Value	445	729
Equal to or Greater than 12 Months Gross Unrealized Loss	20	31
CMBS
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Estimated Fair Value	4,276	1,174
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	74	9
Equal to or Greater than 12 Months Estimated Fair Value	421	413
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 43	$ 33