Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator
Net Income	$ 221.2	$ 205.7	$ 218.6	$ 212.6	$ 233.9	$ 230.2	$ 216.4	$ 213.9	$ 858.1	$ 894.4	$ 284.2
Denominator (000s)
Weighted Average Common Shares - Basic									264,725,800	281,355,900	302,399,800
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards									1,223,400	400,900	1,171,200
Weighted Average Common Shares - Assuming Dilution									265,949,200	281,756,800	303,571,000
Net Income Per Common Share
Earnings Per Share, Basic	$ 0.85	$ 0.78	$ 0.82	$ 0.79	$ 0.86	$ 0.83	$ 0.76	$ 0.74	$ 3.24	$ 3.18	$ 0.94
Earnings Per Share, Diluted	$ 0.84	$ 0.78	$ 0.82	$ 0.79	$ 0.85	$ 0.83	$ 0.76	$ 0.73	$ 3.23	$ 3.17	$ 0.94
Retained Earnings
Numerator
Net Income									$ 858.1	$ 894.4	$ 284.2