Debt (Letter of Credit) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 771	$ 763
Corporate Revolving Facility [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	385	440
CDH [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	256	193
Various Project Financing Facilities [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 130	$ 130