Common Shares - Additional Information (Detail) (CAD) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Feb. 20, 2013 2013 Program
Common Shares [Line Items]
Maximum value of common shares to be repurchased		250.0
Maximum shares of common shares to be repurchased		15,239,531
Percentage of outstanding shares, regulatory maximum for repurchase		10.00%
Share repurchase program expiration date	Feb. 25, 2014