Other Current Assets (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of other current assets
Restricted cash of subsidiaries	$ 86	$ 56
Development advances	72	68
Sales and use tax receivables	45	48
Prepaid expenses	20	15
Assets held for sale	16	16
Derivative assets	3	10
Other	10	7
Other current assets, Total	$ 252	$ 220