Investments (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total Assets	$ 141	$ 148
Total Liabilities	7	9
Partnership [Member]
Variable Interest Entity [Line Items]
Total Assets	109	116
Total Liabilities	1	3
Other
Variable Interest Entity [Line Items]
Total Assets	32	32
Total Liabilities	$ 6	$ 6