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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Income Taxes [Abstract]          
Income tax expense $ 74.4 $ 54.8 $ 128.0 $ 104.3  
Income tax expense, percentage of pre-tax income 32.40% 31.80% 30.00% 32.00%  
Federal statutory tax rate 35.00% 35.00% 35.00% 35.00%  
Total gross unrecognized tax benefits 97.2   97.2   98.1
Unrecognized tax benefits, period increase (decrease)     (0.9)    
Unrecognized tax benefits, if recognized, would reduce the Company's effective tax rate 92.9   92.9   93.8
Gross interest related to unrecognized tax benefit accrued $ 8.8   $ 8.8   $ 7.9