Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2012 Share Repurchase Program Expire In January 2014 [Member]	Sep. 30, 2013 Share Repurchase Program Expire In January 2014 [Member]	Mar. 31, 2011 Share Repurchase Program Expire In August 2012 [Member]	Sep. 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	$ 32.35		$ 32.35
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	2,800,000	100,000	2,400,000
Stock Repurchase Program, Authorized Amount						$ 750.0		$ 1,000.0
Stock Repurchase Program Remaining Authorized Repurchase Amount							281.6		0
Shares Repurchased Cost Commissions		0.1	0.1	0.4	0.6
Treasury Stock, Shares, Acquired	2,500,000	5,100,000	9,800,000	18,600,000	23,600,000
Treasury Stock, Value, Acquired, Cost Method	$ 75.0	$ 100.2	$ 268.5	$ 400.5	$ 500.6
Preferred stock, authorized	25,000,000		25,000,000
Preferred stock, par value	$ 0.10		$ 0.10
Preferred stock, issued	0		0