Investments (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total Assets	$ 473	$ 148
Total Liabilities	6	9
Partnership [Member]
Variable Interest Entity [Line Items]
Total Assets	109	116
Total Liabilities	0	3
Consolidated Entities [Member]
Variable Interest Entity [Line Items]
Total Assets	333	0
Total Liabilities	1	0
Other
Variable Interest Entity [Line Items]
Total Assets	31	32
Total Liabilities	$ 5	$ 6