Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Other items, net	$ (0.7)	$ 0.8	$ (5.8)	$ 13.9
Interest expense	(50.8)	(51.9)	(149.0)	(177.3)
(Loss)/Earnings before income taxes	38.9	9.4	119.5	25.4
Income tax expense	(9.9)	(0.2)	(31.0)	(7.7)
Net earnings/(loss)	29.8	7.4	(41.8)	4.9
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net earnings/(loss)	(1.5)	0.6	(3.5)	2.3
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	1.8	1.9	4.5	6.7
Interest expense	1.6	0.2	(2.7)	0.4
(Loss)/Earnings before income taxes	(0.1)	2.1	1.2	7.1
Income tax expense	0.0	(0.4)	(0.3)	(1.6)
Net earnings/(loss)	(0.1)	1.7	0.9	5.5
Amortization of defined benefit pension items | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial loss	1.9	(1.3)	(5.7)	(3.8)
Income tax expense	(0.5)	0.2	1.3	0.6
Net earnings/(loss)	$ (1.4)	$ (1.1)	$ (4.4)	$ (3.2)