Investments (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total Assets	$ 240	$ 202
Total Liabilities	6	6
Renewable energy partnership
Variable Interest Entity [Line Items]
Total Assets	103	102
Total Liabilities	0	0
Investment funds
Variable Interest Entity [Line Items]
Total Assets	117	79
Total Liabilities	1	1
Other
Variable Interest Entity [Line Items]
Total Assets	20	21
Total Liabilities	$ 5	$ 5