Investments (Unconsolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Carrying Amount Asset	$ 12,863	$ 15,373
Carrying Amount Liability	13,669	15,661
Other limited partnership interests
Variable Interest Entity [Line Items]
Carrying Amount Asset	1,491	1,367
Carrying Amount Liability	2,287	1,647
Real estate joint ventures
Variable Interest Entity [Line Items]
Carrying Amount Asset	17	35
Carrying Amount Liability	22	38
Other Investments [Member]
Variable Interest Entity [Line Items]
Carrying Amount Asset	61	57
Carrying Amount Liability	66	62
Structured securities
Variable Interest Entity [Line Items]
Carrying Amount Asset	10,789	13,453
Carrying Amount Liability	10,789	13,453
U.S. and foreign corporate
Variable Interest Entity [Line Items]
Carrying Amount Asset	505	461
Carrying Amount Liability	$ 505	$ 461