Investments (Unconsolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Carrying Amount Asset	$ 54,192	$ 56,381
Carrying Amount Liability	58,700	60,429
Other limited partnership interests
Variable Interest Entity [Line Items]
Carrying Amount Asset	4,941	4,834
Carrying Amount Liability	9,187	8,543
Other invested assets
Variable Interest Entity [Line Items]
Carrying Amount Asset	2,300	2,291
Carrying Amount Liability	2,557	2,625
Other
Variable Interest Entity [Line Items]
Carrying Amount Asset	41	82
Carrying Amount Liability	46	87
Structured securities (RMBS, CMBS, and ABS)
Variable Interest Entity [Line Items]
Carrying Amount Asset	45,555	47,614
Carrying Amount Liability	45,555	47,614
U.S. corporate and foreign corporate securities
Variable Interest Entity [Line Items]
Carrying Amount Asset	1,355	1,560
Carrying Amount Liability	$ 1,355	$ 1,560