Quarterly report pursuant to Section 13 or 15(d)

Earnings Per Share - Additional information (Detail)

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Earnings Per Share - Additional information (Detail)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Stock Options
       
Earnings Per Share Disclosure [Line Items]        
Stock options excluded from computation of earnings per share 0.9 0.9 0.9 0.9
Performance-Based | Restricted Stock Units (RSUs)
       
Earnings Per Share Disclosure [Line Items]        
Stock options excluded from computation of earnings per share 0.4 0.3 0.4 0.3