Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Intangible Assets (Textual)
Amortization expense of intangible assets	$ 18	$ 22	$ 25
Future Amortization Expense
Future amortization expense, year one	20
Future amortization expense, year two	20
Future amortization expense, year three	20
Future amortization expense, year four	20
Future amortization expense, year five	$ 20