Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 535.5	$ 825.7	$ 729.7
Other comprehensive income (loss):
Pension and other postretirement benefit plan adjustments (net of tax expense (benefit) of $87.2, $159.3, and ($73.7))	268.9	312.8	(142.7)
Currency translation adjustments	(48.3)	57.2	(42.5)
Net change in unrealized gains and losses on cash flow hedges (net of tax expense (benefit) of $6.6, ($2.8), and ($6.7))	18.8	(10.3)	(19.0)
Net change in unrealized gains and losses on available-for-sale investments	(2.1)	(0.1)	0.0
Other comprehensive income (loss)	237.3	359.6	(204.2)
Comprehensive income	$ 772.8	$ 1,185.3	$ 525.5