Debt, Bank Debt and Credit Facilities (Details)	3 Months Ended			3 Months Ended					3 Months Ended							0 Months Ended	1 Months Ended
	Mar. 31, 2012 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2011 USD ($)	Mar. 31, 2012 U S Revolver [Member] USD ($)	Mar. 31, 2011 U S Revolver [Member] USD ($)	Dec. 31, 2011 U S Revolver [Member] USD ($)	Mar. 31, 2012 U S Revolver Letter of Credit [Member] USD ($)	Dec. 31, 2011 U S Revolver Letter of Credit [Member] USD ($)	Mar. 31, 2012 Canadian Revolver [Member] CAD	Mar. 31, 2011 Canadian Revolver [Member] CAD	Dec. 31, 2011 Canadian Revolver [Member] CAD	Mar. 31, 2012 Canadian Revolver Letter of Credit [Member] CAD	Dec. 31, 2011 Canadian Revolver Letter of Credit [Member] CAD	Mar. 31, 2012 Other Letter of Credit [Member] USD ($)	Dec. 31, 2011 Other Letter of Credit [Member] USD ($)	May 04, 2012 Other Debt [Member] USD ($)	Apr. 30, 2012 Other Debt [Member] USD ($)	Mar. 31, 2012 Maximum [Member] U S Revolver [Member]
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 500,000,000			$ 3,000,000,000					115,000,000
Line of credit facility, expiration date	June 2012			December 2016					December 2012
Letters of credit outstanding	500,000,000		300,000,000	0		0	153,000,000	119,000,000	0		0	20,000,000	20,000,000	456,000,000	391,000,000
Accounts Receivable Sales Facility
Balance as of beginning of period	250,000,000	100,000,000
Proceeds from the sale of receivables	0	0															850,000,000
Repayments	(150,000,000)	0														(500,000,000)
Balance as of end of period	100,000,000	100,000,000
Credit Facilities (Textual)
Debt to capitalization ratios as per terms of revolver				0.27		0.29												0.60
Borrowings from long-term lines of credit				0	0				0	0
Repayments of long-term lines of credit				0	0				0	0
Accounts Receivable Sales Facility (Textual)
Maximum eligible trade receivables	$ 1,000,000,000
Extended term of accounts receivable sales facility	June 2012