Supplemental Cash Flow Information Supplemental Cash Flow Information (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Significant Noncash Transactions [Line Items]
Change in capital expenditures not paid	$ (22)	$ 47	$ 27