Debt (Receivables-Backed Facility) (Details) (USD $)				0 Months Ended	3 Months Ended
	Mar. 31, 2012 Subsidiary [Member]	Dec. 31, 2011 Subsidiary [Member]	Mar. 31, 2012 Receivables Securitization Facility [Member]	Feb. 21, 2012 Receivables Securitization Facility [Member] Receivables-Backed Facility [Member]	Mar. 31, 2012 Receivables Securitization Facility [Member] Receivables-Backed Facility [Member]	Mar. 31, 2012 Receivables Securitization Facility [Member] Receivables-Backed Facility And Standby Letters Of Credit [Member]
Debt Instrument [Line Items]
Letters of credit outstanding amount			$ 245,500,000
Letter of credit facility, maximum borrowing capacity					600,000,000	300,000,000
Value of receivables sold to asset securitization facility					886,900,000
Proceeds from accounts receivable securitization					874,500,000
Repayments of accounts receivable securitization					855,000,000
Average daily balance under facility					271,200,000
Line of credit, amount outstanding	279,490,000	260,000,000			279,500,000
Issuance of standby letter of credit				$ 80,000,000