Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator
Net Income	$ 205.7	$ 230.2	$ 636.9	$ 660.5
Denominator (000s)
Weighted Average Common Shares - Basic	262,945,900	278,354,400	265,932,600	284,012,800
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,314,100	156,600	1,161,100	478,400
Weighted Average Common Shares - Assuming Dilution	264,260,000	278,511,000	267,093,700	284,491,200
Net Income Per Common Share
Earnings Per Share, Basic	$ 0.78	$ 0.83	$ 2.39	$ 2.33
Earnings Per Share, Diluted	$ 0.78	$ 0.83	$ 2.38	$ 2.32
Retained Earnings
Numerator
Net Income	$ 205.7	$ 230.2	$ 636.9	$ 660.5