Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Policies (Detail)

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Summary of Significant Policies (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Schedule Of Significant Accounting Policies [Line Items]        
Anti-dilutive securities excluded from earnings per share, per share value 6,728,789   6,325,138  
Amounts of tax included on a gross basis $ 36.1 $ 34.1 $ 67.5 $ 66.6