Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator
Net Income	$ 218.6	$ 216.4	$ 431.2	$ 430.3
Denominator (000s)
Weighted Average Common Shares - Basic	265,560,400	283,316,600	267,452,000	286,874,500
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,175,900	424,000	1,084,600	639,300
Weighted Average Common Shares - Assuming Dilution	266,736,300	283,740,600	268,536,600	287,513,800
Net Income Per Common Share
Earnings Per Share, Basic	$ 0.82	$ 0.76	$ 1.61	$ 1.50
Earnings Per Share, Diluted	$ 0.82	$ 0.76	$ 1.61	$ 1.50
Retained Earnings
Numerator
Net Income	$ 218.6	$ 216.4	$ 431.2	$ 430.3