Share-Based Compensation Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	9 Months Ended	1 Months Ended			1 Months Ended	3 Months Ended			1 Months Ended
	Mar. 31, 2012	Sep. 30, 2012 CompensationPlan	Apr. 18, 2012 Plan Of 2012	Sep. 30, 2012 Plan Of 2012	Sep. 30, 2012 Directors Plan	Apr. 18, 2012 Employee Stock Purchase Plan	Mar. 31, 2012 Performance Restricted Stock Units	Mar. 31, 2012 Performance Restricted Stock Units Minimum	Mar. 31, 2012 Performance Restricted Stock Units Maximum	Jul. 31, 2012 Management Stock Purchase Program	Jul. 31, 2011 Management Stock Purchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of remaining shares that may be issued				5,904,609	49,099
Additional shares authorized			2,750,000			750,000
Reduction in the number of total shares for each stock option or stock appreciation rights granted, per share			1
Reduction in the number of total shares for each award of other share based awards, per share			2.87
Number of employee stock purchase programs		2
Fair value assumptions, risk-free interest rate	0.41%									0.16%	0.12%
Fair value assumptions, dividend yield	0.85%									0.90%	0.80%
Fair value assumptions, expected life in years	2 years 9 months 29 days									7 months 6 days	7 months 6 days
Awards requisite service period, in years							3 years
Percentage of target payout of employee varying from actual payout under award								0.00%	200.00%
Number of shares granted in period										200,000	200,000
Fair value per share of shares granted in period										$ 38.33	$ 38.25
Fair value assumptions, expected volatility										20.00%	16.00%
Unrecognized compensation expenses related to share-based payment arrangements		$ 78.3
Weighted-average period of recognizing unrecognized compensation expenses related to share-based compensation, in years		2 years