Consolidated Statements of Shareholders' Investment - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Beginning Balance		$ 1,455.3		$ 1,804.9	$ 1,455.3	$ 1,804.9	$ 2,088.2
Net income	$ 159.6	$ 116.2	$ 136.3	$ 139.8	531.4	135.4	294.5
Total other comprehensive income (loss)					(27.5)	(119.2)	(67.9)
Cash dividends declared ($0.87 per share for 2014, $0.94 per share for 2015 and $ 1.02 per share for 2016)					(75.9)	(70.6)	(66.4)
Issuance of common stock					67.6	77.3	109.3
Share-based compensation					90.0	81.8	71.6
Purchases of common stock					(406.9)	(498.7)	(659.6)
Tax benefit relating to share-based compensation plans					41.1	44.4	35.2
Ending Balance	$ 1,675.1		$ 1,455.3		$ 1,675.1	$ 1,455.3	$ 1,804.9
Common Stock
Beginning Balance (Shares)		73,697,371		74,893,483	73,697,371	74,893,483	77,436,263
Beginning Balance		$ 18.4		$ 18.7	$ 18.4	$ 18.7	$ 19.4
Issuance of common stock					$ 0.3	$ 0.4	$ 0.4
Issuance of common stock (in shares)					1,201,880	1,549,177	1,954,647
Purchases of common stock (in shares)					(2,000,000)	(2,745,289)	(4,497,427)
Purchases of common stock					$ (0.5)	$ (0.7)	$ (1.1)
Ending Balance (in shares)	72,899,251		73,697,371		72,899,251	73,697,371	74,893,483
Ending Balance	$ 18.2		$ 18.4		$ 18.2	$ 18.4	$ 18.7
Capital In Excess Of Par Value
Beginning Balance		2,148.4		1,945.3	2,148.4	1,945.3	1,729.6
Issuance of common stock					67.3	76.9	108.9
Share-based compensation					90.0	81.8	71.6
Purchases of common stock					0.0	0.0	0.0
Tax benefit relating to share-based compensation plans					41.1	44.4	35.2
Ending Balance	2,346.8		2,148.4		2,346.8	2,148.4	1,945.3
Accumulated Deficit / Retained Earnings
Beginning Balance		(503.5)		(70.3)	(503.5)	(70.3)	360.1
Net income					531.4	135.4	294.5
Cash dividends declared ($0.87 per share for 2014, $0.94 per share for 2015 and $ 1.02 per share for 2016)					(75.9)	(70.6)	(66.4)
Purchases of common stock					(406.4)	(498.0)	(658.5)
Ending Balance	(454.4)		(503.5)		(454.4)	(503.5)	(70.3)
Accumulated Other Comp. (Loss) Inc.
Beginning Balance		$ (208.0)		$ (88.8)	(208.0)	(88.8)	(20.9)
Total other comprehensive income (loss)					(27.5)	(119.2)	(67.9)
Ending Balance	$ (235.5)		$ (208.0)		$ (235.5)	$ (208.0)	$ (88.8)