Annual report pursuant to Section 13 and 15(d)

Share-Based and Cash-Based Incentive Compensation - Additional Information (Detail)

v2.4.0.6
Share-Based and Cash-Based Incentive Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock available for award under the plans 1,393,602    
Percentage of RSUs affected by performance 100.00% 100.00% 100.00%
Directors Compensation Plan
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock available for award under the plans 546,829    
Restricted Stock
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted, grant date fair value 0.4 0.5 0.4
Shares vested, grant date fair value 0.5 7.9 8.1
Unrecognized share-based compensation expense 0.5    
Recognition period for unrecognized compensation expense April 2015    
Restricted Stock Units (RSUs)
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted, grant date fair value 14.3 14.4 12.0
Shares vested, grant date fair value 20.0    
Unrecognized share-based compensation expense 11.4    
Recognition period for unrecognized compensation expense November 2014