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
	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2011	Jun. 30, 2010	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Stockholders Equity Note [Line Items]
Outstanding Performance restricted stock units, threshold stock price	$ 26.00				$ 26.00
Antidilutive common shares not included in the computation of dilutive earnings per share	2,800,000	2,400,000			2,400,000	2,100,000
Authorized repurchase of common stock, value	$ 750.0		$ 1,000.0	$ 500.0
Treasury Stock Acquired, Shares	5,100,000				18,600,000		17,700,000
Common stock repurchased	100.2				400.5		419.9
Shares repurchased cost, Commissions	0.1				0.4		0.3
Stock Repurchase Program Remaining Authorized Repurchase Amount	650.0
Treasury Stock Shares Retired			7,700,000
Preferred stock, authorized	25,000,000				25,000,000
Preferred stock, par value	$ 0.10				$ 0.10
Preferred stock, issued	0				0
Share Repurchase Program Expire in May 2011 [Member]
Stockholders Equity Note [Line Items]
Treasury Stock Acquired, Shares		600,000	7,100,000			7,700,000
Common stock repurchased			$ 200.0
Minimum [Member]
Stockholders Equity Note [Line Items]
Outstanding stock options, exercise prices range	$ 11.37				$ 11.37
Outstanding Nonvested stock awards, grant prices range	$ 19.38				$ 19.38
Maximum [Member]
Stockholders Equity Note [Line Items]
Outstanding stock options, exercise prices range	$ 26.29				$ 26.29
Outstanding Nonvested stock awards, grant prices range	$ 26.31				$ 26.31