Debt (Letter of Credit) (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount		$ 1,369	$ 1,069
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	[1]	953	629
CDH [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount		235	244
Various Project Financing Facilities [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount		$ 181	$ 196

[1] The Corporate Revolving Facility represents our primary revolving facility.