Equity Share Repurchase Program (Details) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended			9 Months Ended		10 Months Ended
		Oct. 20, 2017 USD ($) shares	Aug. 31, 2017 USD ($) $ / shares shares	Oct. 20, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Oct. 20, 2017 USD ($) $ / shares shares	May 31, 2015 USD ($)
Equity, Class of Treasury Stock [Line Items]
Shares repurchased					$ 200.0	$ 40.6	$ 320.4	$ 99.8
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased									$ 320.4
Shares repurchased (shares) | shares									3,241,978
Average price of shares repurchased | $ / shares									$ 98.83
2015 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Maximum amount of share repurchase program										$ 500.0
2017 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Maximum amount of share repurchase program			$ 800.0
Expiration date of share repurchase program			Jun. 30, 2020
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Maximum amount of share repurchase program			$ 200.0
Number of ASR agreements entered into by the Company					2
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased				$ 200.0
Shares repurchased (shares) | shares				1,901,769
Weighted-average price of all shares repurchased under ASR Agreement(s) | $ / shares				$ 105.17
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | Initial Shares Delivered [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased			$ 170.0
Shares repurchased (shares) | shares			1,598,796
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | Additional Shares Delivered [Member] | Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased				$ 30.0
Shares repurchased (shares) | shares				302,973
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased			$ 100.0
Shares repurchased (shares) | shares			950,879
Weighted-average price of all shares repurchased under ASR Agreement(s) | $ / shares			$ 105.17
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 1 [Member] | Initial Shares Delivered [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased			$ 85.0
Shares repurchased (shares) | shares			799,398
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 1 [Member] | Additional Shares Delivered [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased			$ 15.0
Shares repurchased (shares) | shares			151,481
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 2 [Member] | Additional Paid-in Capital [Member]
Equity, Class of Treasury Stock [Line Items]
Forward contract recorded by the Company for portion of accelerated share repurchase agreement(s) not yet settled.					$ 15.0		$ 15.0
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 2 [Member] | Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased				$ 100.0
Shares repurchased (shares) | shares				950,890
Weighted-average price of all shares repurchased under ASR Agreement(s) | $ / shares				$ 105.16
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 2 [Member] | Initial Shares Delivered [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased			$ 85.0
Shares repurchased (shares) | shares			799,398
2017 Share Repurchase Program [Member] | Accelerated Share Repurchase Program [Member] | ASR Agreement 2 [Member] | Additional Shares Delivered [Member] | Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	[1]	$ 15.0
Shares repurchased (shares) | shares		151,492

[1] The remaining $15.0 million as of September 30, 2017 was recorded as a forward contract indexed to the Company’s own common stock and included in capital surplus within Additional paid-in capital in the accompanying Consolidated Balance Sheet, and was subsequently settled in October 2017.