Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 1,976.5
Total other comprehensive income (loss), net of tax	(29.6)	$ (10.5)
Balance at end of period	1,980.3
Employee Pension and Postretirement Benefits, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(73.9)	(46.4)
Other comprehensive income (loss) before reclassifications	0.0	0.0
Amounts reclassified from accumulated other comprehensive income	0.8	0.5
Total other comprehensive income (loss), net of tax	0.8	0.5
Balance at end of period	(73.1)	(45.9)
Cumulative Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(101.1)	(98.1)
Other comprehensive income (loss) before reclassifications	(30.4)	(11.2)
Amounts reclassified from accumulated other comprehensive income	0.0	0.0
Total other comprehensive income (loss), net of tax	(30.4)	(11.2)
Balance at end of period	(131.5)	(109.3)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period		0.1
Other comprehensive income (loss) before reclassifications		0.2
Amounts reclassified from accumulated other comprehensive income		0.0
Total other comprehensive income (loss), net of tax		0.2
Balance at end of period		0.3
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(175.0)	(144.4)
Other comprehensive income (loss) before reclassifications	(30.4)	(11.0)
Amounts reclassified from accumulated other comprehensive income	0.8	0.5
Total other comprehensive income (loss), net of tax	(29.6)	(10.5)
Balance at end of period	$ (204.6)	$ (154.9)