Earnings per Share - Reconciliation of common shares (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Basic average common shares outstanding (in shares)	88.2	91.3	87.7	91.9
Impact of restricted shares, restricted share units and performance share units (in shares)	1.1	1.2	1.2	1.6
Impact of convertible notes (in shares)	2.7	0.0	1.3	0.0
Diluted average common shares outstanding (in shares)	92.0	92.5	90.2	93.5