Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other financing items, net	$ (1.5)	$ 0.6
Interest expense	(13.3)	(12.9)
Total before tax	134.1	94.5
Tax (expense)/benefit	(38.5)	(29.0)
Net earnings	95.6	65.5
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net earnings	(1.4)	0.5
Gains and losses on cash flow hedges | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other financing items, net	0.5	2.8
Interest expense	(0.7)	(0.7)
Total before tax	(0.2)	2.1
Tax (expense)/benefit	0.2	(0.4)
Net earnings	0.0	1.7
Amortization of defined benefit pension items | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial loss	(2.0)	(1.6)
Settlement loss	0.0	(0.1)
Total before tax	(2.0)	(1.7)
Tax (expense)/benefit	0.6	0.5
Net earnings	$ (1.4)	$ (1.2)