Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax	$ (1,040.7)	$ (775.6)	$ (1,040.7)	$ (775.6)	$ (1,015.9)	$ (948.0)	$ (793.2)	$ (817.7)
Other comprehensive income (loss) before reclassifications, net of tax	(36.3)	3.1	(117.0)	13.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	11.5	14.5	24.3	28.8
Other comprehensive income (loss), net of tax	(24.8)	17.6	(92.7)	42.1
Pension and other postretirement benefit plan adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax	(874.6)	(794.7)	(874.6)	(794.7)	(891.8)	(909.4)	(809.2)	(823.8)
Other comprehensive income (loss) before reclassifications, net of tax	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss, net of tax	17.2	14.5	34.8	29.1
Other comprehensive income (loss), net of tax	17.2	14.5	34.8	29.1
Accumulated currency translation adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax	(213.1)	23.1	(213.1)	23.1	(145.4)	(52.5)	18.0	8.8
Other comprehensive income (loss) before reclassifications, net of tax	(67.7)	5.1	(160.6)	14.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	0	0	0	0
Other comprehensive income (loss), net of tax	(67.7)	5.1	(160.6)	14.3
Net unrealized gains (losses) on cash flow hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax	47.0	(4.0)	47.0	(4.0)	21.3	13.9	(2.0)	(2.7)
Other comprehensive income (loss) before reclassifications, net of tax	31.4	(2.0)	43.6	(1.0)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(5.7)	0	(10.5)	(0.3)
Other comprehensive income (loss), net of tax	$ 25.7	$ (2.0)	$ 33.1	$ (1.3)