Investments (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Gain (Loss) on Securitization of Financial Assets	$ 20
Total Assets	148	$ 59
Total Liabilities	9	12
Operating joint venture
Variable Interest Entity [Line Items]
Total Assets	116	0
Total Liabilities	3	0
CSEs (assets (primarily loans) and liabilities (primarily debt))
Variable Interest Entity [Line Items]
Total Assets	7	9
Total Liabilities	6	12
Other
Variable Interest Entity [Line Items]
Total Assets	25	50
Total Liabilities	$ 0	$ 0