Pension and Other Postretirement Benefits (Details)	3 Months Ended
	Mar. 31, 2012 plan
Pension Plans
Pension and Other Postretirement Benefits
Number of funded plans	4
Number of funded plans closed to new employees	3
U.S plan
Pension and Other Postretirement Benefits
Number of funded plans	2
Canadian plan
Pension and Other Postretirement Benefits
Number of funded plans	2
Number of funded plans closed to new employees	1