Summary of Significant Accounting Policies (Interest Expense and Amortization of Deferred Financing Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Interest expense on debt obligations	$ 635	$ 582	$ 501
Amortization of deferred financing costs and adjustments on long-term debt, net	21	19	19
Capitalized Interest	(15)	(12)	(7)
Other	1	2	2
Total	$ 642	$ 591	$ 515