Shareholders' Equity (Details) $ / shares in Units, shares in Millions, number in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017 shares	Mar. 31, 2017 USD ($) $ / shares shares	Mar. 31, 2016 USD ($)
Stockholders' Equity Note [Abstract]
Treasury Stock, Shares, Acquired		1.7
Treasury Stock Acquired, Average Cost Per Share (in USD per share) | $ / shares		$ 76.32
Total Cost of Treasury Shares Acquired | $		$ 133.1	$ 0.0
Tangible Equity Units, Units exchanged	0.9
Stock Issued During Period, Shares, Conversion of Tangible Equity Units	1.5