Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Share Repurchase Program Expire In January 2014 [Member]	Jun. 30, 2012 Share Repurchase Program Expire In January 2014 [Member]	Mar. 31, 2013 Share Repurchase Program Expire In August 2012 [Member]	Mar. 31, 2011 Share Repurchase Program Expire In August 2012 [Member]	Mar. 31, 2013 shares repurchased on the open market [Member]	Mar. 31, 2012 shares repurchased on the open market [Member]	Dec. 31, 2012 shares repurchased on the open market [Member]
Stockholders Equity Note [Line Items]
Oustanding Stock Options, grant price range, lower limit	$ 11.37
Oustanding Stock Options, grant price range, upper limit	$ 26.29
Outstanding Nonvested stock awards, grant prices range, lower limit	$ 19.38
Outstanding Nonvested stock awards, grant prices range, upper limit	$ 26.31
Antidilutive common shares not included in the computation of dilutive earnings per share	400,000	2,200,000
Stock Repurchase Program, Authorized Amount				$ 750.0		$ 1,000.0
Stock Repurchase Program Remaining Authorized Repurchase Amount			$ 454.9		$ 0
Treasury Stock, Shares, Acquired							3,700,000	7,500,000	23,600,000
Preferred stock, authorized	25,000,000
Preferred stock, par value	$ 0.10
Preferred stock, issued	0