Investments (Unconsolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Carrying Amount Asset	$ 56,381	$ 55,832
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	60,429	60,695
Other limited partnership interests
Variable Interest Entity [Line Items]
Carrying Amount Asset	4,834	4,714
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	8,543	8,990
Other invested assets
Variable Interest Entity [Line Items]
Carrying Amount Asset	2,291	2,206
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	2,625	2,777
Other
Variable Interest Entity [Line Items]
Carrying Amount Asset	82	199
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	87	215
Structured securities (RMBS, CMBS, and ABS)
Variable Interest Entity [Line Items]
Carrying Amount Asset	47,614	46,773
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	47,614	46,773
U.S. corporate and foreign corporate securities
Variable Interest Entity [Line Items]
Carrying Amount Asset	1,560	1,940
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 1,560	$ 1,940