Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ (1,588.9)	$ (1,339.0)	$ (1,538.8)	$ (1,334.6)
Other comprehensive (loss) income before reclassifications	58.4	1.6	(15.3)	(16.3)
Amounts reclassified from accumulated other comprehensive loss	22.5	11.7	46.1	25.2
Other comprehensive income (loss)	80.9	13.3	30.8	8.9
Balance at end of period	(1,508.0)	(1,325.7)	(1,508.0)	(1,325.7)
Pension and other postretirement benefit plan adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,215.3)	(1,078.7)	(1,239.8)	(1,097.1)
Other comprehensive (loss) income before reclassifications	0.0	0.0	0.7	0.0
Amounts reclassified from accumulated other comprehensive loss	23.8	18.4	47.6	36.8
Other comprehensive income (loss)	23.8	18.4	48.3	36.8
Balance at end of period	(1,191.5)	(1,060.3)	(1,191.5)	(1,060.3)
Accumulated currency translation adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(381.1)	(276.8)	(294.9)	(252.4)
Other comprehensive (loss) income before reclassifications	60.8	7.4	(25.4)	(17.0)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	60.8	7.4	(25.4)	(17.0)
Balance at end of period	(320.3)	(269.4)	(320.3)	(269.4)
Net unrealized gains (losses) on cash flow hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	7.5	16.5	(4.1)	14.9
Other comprehensive (loss) income before reclassifications	(2.3)	(5.8)	9.5	0.7
Amounts reclassified from accumulated other comprehensive loss	(1.3)	(6.7)	(1.5)	(11.6)
Other comprehensive income (loss)	(3.6)	(12.5)	8.0	(10.9)
Balance at end of period	3.9	4.0	3.9	4.0
Net unrealized gains (losses) on available-for-sale investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	0.0	0.0	0.0	0.0
Other comprehensive (loss) income before reclassifications	(0.1)	0.0	(0.1)	0.0
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	(0.1)	0.0	(0.1)	0.0
Balance at end of period	$ (0.1)	$ 0.0	$ (0.1)	$ 0.0