Summary of Significant Accounting Policies (Deferred Financing Costs and Revenue Recognition) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Amortization of deferred financing costs	$ 19	$ 15	$ 5
Proceeds from U.S. Treasury Grants	$ 44	$ 388	$ 92