Net Income Per Common Share (Detail) (USD $) In Millions, except Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Numerator
Net Income	$ 205.6	$ 220.8	$ 660.8	$ 660.3
Denominator (000s)
Weighted Average Common Shares - Basic	298,185,800	323,083,500	305,694,500	328,828,600
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	987,100	1,383,500	1,223,900	1,344,500
Weighted Average Common Shares - Assuming Dilution	299,172,900	324,467,000	306,918,400	330,173,100
Net Income Per Common Share
Basic	$ 0.69	$ 0.68	$ 2.16	$ 2.01
Assuming Dilution	$ 0.69	$ 0.68	$ 2.15	$ 2.00
Retained Earnings [Member]
Numerator
Net Income			$ 660.8