Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Disclosure [Line Items]
Net Income	$ 230.2	$ 202.0	$ 660.5	$ 653.2
Denominator (000s)
Weighted Average Common Shares - Basic	278,354,400	298,185,800	284,012,800	305,694,500
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	156,600	987,100	478,400	1,223,900
Weighted Average Common Shares - Assuming Dilution	278,511,000	299,172,900	284,491,200	306,918,400
Net Income Per Common Share
Basic	$ 0.83	$ 0.68	$ 2.33	$ 2.14
Assuming Dilution	$ 0.83	$ 0.68	$ 2.32	$ 2.13