Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Policies (Detail)

Summary of Significant Policies (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Schedule Of Significant Accounting Policies [Line Items]    
Anti-dilutive securities excluded from earnings per share, per share value 5,794,079  
Amounts of tax included on a gross basis $ 31.4 $ 32.5