Supplemental Guarantor Information (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 6.9 percent senior notes due June 2013	Dec. 31, 2010 6.9 percent senior notes due June 2013	Dec. 31, 2011 5.4 percent senior notes due January 2015	Dec. 31, 2010 5.4 percent senior notes due January 2015	Dec. 31, 2011 8.4 percent senior notes due May 2017	Dec. 31, 2010 8.4 percent senior notes due May 2017	Dec. 31, 2011 6.6 percent senior notes due May 2020	Dec. 31, 2010 6.6 percent senior notes due May 2020
Supplemental Guarantor Information
Percentage ownership of Guarantor Subsidiaries (as a percent)	100.00%
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage (as a percent)		6.90%	6.90%	5.40%	5.40%	8.40%	8.40%	6.60%	6.60%