Other Current Assets (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of other current assets
Other current assets	$ 208	$ 168
Development advances [Member]
Summary of other current assets
Other current assets	67	63
Sales and use tax receivables [Member]
Summary of other current assets
Other current assets	54	49
Restricted cash of subsidiaries [Member]
Summary of other current assets
Other current assets	37	16
Prepaid Expenses [Member]
Summary of other current assets
Other current assets	19	15
Assets held for sale [Member]
Summary of other current assets
Other current assets	16	16
Derivative assets [member]
Summary of other current assets
Other current assets	8	2
Other [Member]
Summary of other current assets
Other current assets	$ 7	$ 7