Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator
Net Income	$ 203.8	$ 219.1	$ 641.0	$ 684.3
Denominator (000s)
Weighted Average Common Shares - Basic	245,400,000	253,586,100	248,372,900	256,573,600
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	924,400	1,209,400	855,200	1,210,100
Weighted Average Common Shares - Assuming Dilution	246,324,400	254,795,500	249,228,100	257,783,700
Net Income Per Common Share
Basic	$ 0.83	$ 0.86	$ 2.58	$ 2.67
Assuming Dilution	$ 0.83	$ 0.86	$ 2.57	$ 2.66