Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,663.6	$ 1,990.1
Other comprehensive loss before reclassifications	146.7	260.0	$ (262.6)
Amounts reclassified from accumulated other comprehensive loss	90.6	99.6	58.4
Other comprehensive income (loss)	237.3	359.6	(204.2)
Ending balance	1,617.5	2,663.6	1,990.1
Pension and other postretirement benefit plan adjustments, net of tax (Note 12)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(927.0)	(1,239.8)	(1,097.1)
Other comprehensive loss before reclassifications	188.4	215.2	(216.5)
Amounts reclassified from accumulated other comprehensive loss	80.5	97.6	73.8
Other comprehensive income (loss)	268.9	312.8	(142.7)
Ending balance	(658.1)	(927.0)	(1,239.8)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(237.7)	(294.9)	(252.4)
Other comprehensive loss before reclassifications	(48.3)	57.2	(42.5)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive income (loss)	(48.3)	57.2	(42.5)
Ending balance	(286.0)	(237.7)	(294.9)
Net unrealized gains (losses) on cash flow hedges, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14.4)	(4.1)	14.9
Other comprehensive loss before reclassifications	8.7	(12.3)	(3.6)
Amounts reclassified from accumulated other comprehensive loss	10.1	2.0	(15.4)
Other comprehensive income (loss)	18.8	(10.3)	(19.0)
Ending balance	4.4	(14.4)	(4.1)
Net unrealized gains (losses) on available-for-sale investments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.1)	0.0	0.0
Other comprehensive loss before reclassifications	(2.1)	(0.1)	0.0
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive income (loss)	(2.1)	(0.1)	0.0
Ending balance	(2.2)	(0.1)	0.0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,179.2)	(1,538.8)	(1,334.6)
Other comprehensive income (loss)	237.3	359.6	(204.2)
Ending balance	$ (941.9)	$ (1,179.2)	$ (1,538.8)