Earnings Per Share (Details) (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
Earnings per share [Abstract]
Net income	$ 140.4	$ 174.6	$ 288.8	$ 308.6
Average shares outstanding (basic) (in shares)	246,600,000	246,300,000	247,100,000	246,200,000
Common stock equivalents (in shares)	1,500,000	1,400,000	1,500,000	1,600,000
Diluted shares (in shares)	248,100,000	247,700,000	248,600,000	247,800,000
Basic earnings per share (in dollars per share)	$ 0.57	$ 0.71	$ 1.17	$ 1.25
Diluted earnings per share (in dollars per share)	$ 0.57	$ 0.70	$ 1.16	$ 1.25
Treasury Shares [Roll Forward]
Treasury shares at beginning of period (in shares)	15,768,832	16,826,348	16,415,336	17,579,397
Purchase of treasury shares (in shares)	1,500,002	100,000	2,113,455	157,200
Net change in treasury shares owned by participants in nonqualified deferred compensation plans (in shares)	(1,068)	0	52,107	0
Treasury shares issued in satisfaction of stock option exercises and vesting of stock units (in shares)	(266,036)	(87,330)	(1,579,168)	(897,579)
Treasury shares at end of period (in shares)	17,001,730	16,839,018	17,001,730	16,839,018
Average cost of treasury shares acquired (in dollars per share)			$ 60.93	$ 61.77