Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator
Net Income	$ 224.3	$ 239.4	$ 437.2	$ 465.2
Denominator (000s)
Weighted Average Common Shares - Basic	248,318,600	256,790,200	249,885,000	258,092,700
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	873,600	1,119,500	820,500	1,210,400
Weighted Average Common Shares - Assuming Dilution	249,192,200	257,909,700	250,705,500	259,303,100
Net Income Per Common Share
Basic	$ 0.90	$ 0.93	$ 1.75	$ 1.80
Assuming Dilution	$ 0.90	$ 0.93	$ 1.74	$ 1.79