Share Capital (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Treasury stock repurchase limit	$ 750
Treasury Stock, Value, Acquired, Cost Method	190
Treasury Stock, Shares, Retired (in Shares)	4.7
Treasury Stock, Retired, Cost Method, Amount	100.0
Treasury Stock, Value	650.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures (in Shares)	1.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share)	$ 7.62
Minimum Percentage Target Payout Under Performance Unit Grants In Period	0.00%
Maximum Percentage Target Payout Under Performance Unit Grants In Period	200.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares)	0.3
Share Based Compensation Arrangement By Share Based Payment Award Weighted Average Grant Date Fair Value	5.3
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares)	1.3
Share Based Compensation Arrangement By Share Based Payment Award Weighted Average Grant Date Fair Value	25.9
Performance Incentive Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares)	1.5
Maximum Limit Share Payout Under Performance Unit Grants In Period	3.0
Share Based Compensation Arrangement By Share Based Payment Award Restricted Stock Units Grants In Period Weighted Average Grant Date Fair Value	$ 29.0