Capital Stock - Number of Shares Contingently Issuable (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	0.78%	1.95%	2.31%
Expected volatility	34.94%	34.47%	35.02%
Expected dividend yields	0.82%	0.47%	0.60%
Share Appreciation Program 2008 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable upon vesting, maximum amount	0	1,372,000	1,485,000	2,592,000
Shares Issuable Upon Vesting, Minimum Amount	0	0	0
Risk free interest rate	2.98%
Expected volatility	28.31%
Expected dividend yields	0.54%