Consolidated Statements of Shareholders' Investment (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Beginning Balance	$ 2,088.2	$ 1,925.7	$ 1,771.2
Net income	294.5	689.8	530.1
Total other comprehensive income (loss)	(67.9)	60.3	(14.6)
Cash dividends declared ($0.79 per share for 2012, $0.83 per share for 2013 and $0.87 per share for 2014)	(66.4)	(66.4)	(66.9)
Issuance of common stock	109.3	134.2	101.3
Share-based compensation	71.6	61.5	52.0
Purchases of common stock	(659.6)	(738.1)	(458.0)
Tax benefit relating to share-based compensation plans	35.2	21.2	10.6
Ending Balance	1,804.9	2,088.2	1,925.7
Common Stock
Beginning Balance (Shares)	77,436,263	81,697,409	84,543,338
Beginning Balance	19.4	20.4	21.2
Net income	0	0	0
Total other comprehensive income (loss)	0	0	0
Cash dividends declared ($0.79 per share for 2012, $0.83 per share for 2013 and $0.87 per share for 2014)	0	0	0
Issuance of common stock (in shares)	1,954,647	2,298,049	1,889,148
Issuance of common stock	0.4	0.6	0.4
Share-based compensation	0	0	0
Purchases of common stock (in shares)	(4,497,427)	(6,559,195)	(4,735,077)
Purchases of common stock	(1.1)	(1.6)	(1.2)
Tax benefit relating to share-based compensation plans	0	0	0
Ending Balance (in shares)	74,893,483	77,436,263	81,697,409
Ending Balance	18.7	19.4	20.4
Capital In Excess Of Par Value
Beginning Balance	1,729.6	1,513.3	1,349.8
Net income	0	0	0
Total other comprehensive income (loss)	0	0	0
Cash dividends declared ($0.79 per share for 2012, $0.83 per share for 2013 and $0.87 per share for 2014)	0	0	0
Issuance of common stock	108.9	133.6	100.9
Share-based compensation	71.6	61.5	52.0
Purchases of common stock	0	0	0
Tax benefit relating to share-based compensation plans	35.2	21.2	10.6
Ending Balance	1,945.3	1,729.6	1,513.3
Accumulated Deficit / Retained Earnings
Beginning Balance	360.1	473.2	466.8
Net income	294.5	689.8	530.1
Total other comprehensive income (loss)	0	0	0
Cash dividends declared ($0.79 per share for 2012, $0.83 per share for 2013 and $0.87 per share for 2014)	(66.4)	(66.4)	(66.9)
Issuance of common stock	0	0	0
Share-based compensation	0	0	0
Purchases of common stock	(658.5)	(736.5)	(456.8)
Tax benefit relating to share-based compensation plans	0	0	0
Ending Balance	(70.3)	360.1	473.2
Accumulated Other Comp. (Loss) Inc.
Beginning Balance	(20.9)	(81.2)	(66.6)
Net income	0	0	0
Total other comprehensive income (loss)	(67.9)	60.3	(14.6)
Cash dividends declared ($0.79 per share for 2012, $0.83 per share for 2013 and $0.87 per share for 2014)	0	0	0
Issuance of common stock	0	0	0
Share-based compensation	0	0	0
Purchases of common stock	0	0	0
Tax benefit relating to share-based compensation plans	0	0	0
Ending Balance	$ (88.8)	$ (20.9)	$ (81.2)