Capital Structure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Interest paid on debt	$ 15	$ 16	$ 16
Liabilities assumed	34
Other liabilities and accrued expenses	952	849
Limited Partnership
Debt Instrument [Line Items]
Liabilities assumed	56	44
Other liabilities and accrued expenses	22	$ 44
Debt Related to Other Investments
Debt Instrument [Line Items]
Other liabilities and accrued expenses	$ 34