Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2012 Share Repurchase Program Expire In January 2014 [Member]	Jun. 30, 2013 Share Repurchase Program Expire In January 2014 [Member]	Mar. 31, 2011 Share Repurchase Program Expire In August 2012 [Member]	Jun. 30, 2013 Share Repurchase Program Expire In August 2012 [Member]
Stockholders Equity Note [Line Items]
Oustanding Stock Options, grant price range, lower limit	$ 11.37		$ 11.37
Oustanding Stock Options, grant price range, upper limit	$ 26.29		$ 26.29
Outstanding Nonvested stock awards, grant prices range, lower limit	$ 19.38		$ 19.38
Outstanding Nonvested stock awards, grant prices range, upper limit	$ 28.25		$ 28.25
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 23.97
Antidilutive common shares not included in the computation of dilutive earnings per share	0	2,300,000	200,000	2,200,000
Stock Repurchase Program, Authorized Amount						$ 750.0		$ 1,000.0
Stock Repurchase Program Remaining Authorized Repurchase Amount							356.6		0
Treasury Stock, Shares, Acquired	3,600,000	6,000,000	7,300,000	13,500,000	23,600,000
Treasury Stock, Value, Acquired, Cost Method	98.4	125.1	193.5	300.3	500.6
Shares Repurchased Cost Commissions	$ 0.1	$ 0.1	$ 0.1	$ 0.3
Preferred stock, authorized	25,000,000		25,000,000
Preferred stock, par value	$ 0.10		$ 0.10
Preferred stock, issued	0		0