Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Numerator
Net Income	$ 213.9	$ 223.6
Denominator (000s)
Weighted Average Common Shares - Basic	290,429,500	312,742,300
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	854,500	1,590,000
Weighted Average Common Shares - Assuming Dilution	291,284,000	314,332,300
Net Income Per Common Share
Earnings Per Share, Basic	$ 0.74	$ 0.72
Earnings Per Share, Assuming Dilution	$ 0.73	$ 0.71