Debt, Bank Debt and Credit Facilities (Details) In Millions, unless otherwise specified	12 Months Ended								12 Months Ended							12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 U S Revolver [Member] USD ($)	Dec. 31, 2011 U S Revolver [Member] USD ($)	Dec. 31, 2010 U S Revolver [Member] USD ($)	Dec. 31, 2012 U S Revolver Letter of Credit [Member] USD ($)	Dec. 31, 2011 U S Revolver Letter of Credit [Member] USD ($)	Dec. 31, 2012 Canadian Revolver [Member] CAD	Dec. 31, 2011 Canadian Revolver [Member] CAD	Dec. 31, 2010 Canadian Revolver [Member] CAD	Nov. 30, 2012 Canadian Revolver [Member] CAD	Nov. 29, 2012 Canadian Revolver [Member] CAD	Dec. 31, 2012 Canadian Revolver Letter of Credit [Member] CAD	Dec. 31, 2011 Canadian Revolver Letter of Credit [Member] CAD	Dec. 31, 2012 Letter of Credit [Member] USD ($)	Dec. 31, 2011 Letter of Credit [Member] USD ($)	Dec. 31, 2012 Other Revolving Letter of Credit [Member] USD ($)	Dec. 31, 2011 Other Revolving Letter of Credit [Member] USD ($)	Dec. 31, 2012 Other Letter of Credit [Member] USD ($)	Dec. 31, 2011 Other Letter of Credit [Member] USD ($)	Dec. 31, 2012 Maximum [Member] U S Revolver [Member]
Line of Credit Facility
Line of credit facility, maximum borrowing capacity				$ 3,000								50	115			$ 550
Line of credit facility, expiration date (month, year)				December 2016					November 2013							June 2013
Letters of credit outstanding							59	119						10	20	418	300	0	0	275	391
Credit Facilities (Textual)
Debt to capitalization ratios as per terms of revolver				0.23	0.29																	0.60
Borrowings from long-term lines of credit	1,100	0	0	1,100	0	0			0	0	0
Repayments of long-term lines of credit	$ 1,100	$ 4	$ 0	$ 1,100	$ 0	$ 0			0	0	0