Debt (Letter of Credit) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 623		$ 644
Corporate Revolving Facility [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	202	[1]	223	[1]
CDH [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	235		214
Various Project Financing Facilities [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 186		$ 207

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