Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Other items, net	$ (5.1)	$ (3.8)	$ (5.1)	$ 13.1
Interest expense	(47.2)	(77.2)	(98.2)	(125.4)
Earnings before income taxes	21.9	(74.0)	80.6	16.0
Income tax benefit	(8.2)	11.7	(21.1)	(7.5)
Net loss	(117.7)	(73.3)	(71.6)	(2.5)
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net loss	(1.5)	0.8	(2.0)	1.7
Gains and losses on cash flow hedges | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Other items, net	0.8	2.0	2.7	4.8
Interest expense	0.6	0.3	(1.1)	0.2
Earnings before income taxes	0.2	2.3	1.3	5.0
Income tax benefit	0.1	(0.5)	(0.3)	(1.2)
Net loss	0.1	1.8	1.0	3.8
Amortization of defined benefit pension items | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial loss	1.9	(1.2)	(3.8)	(2.5)
Income tax benefit	(0.3)	0.2	0.8	0.4
Net loss	$ (1.6)	$ (1.0)	$ (3.0)	$ (2.1)