Condensed Consolidated Statement of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Pension and other postretirement benefit plan adjustments tax expense	$ 7.2	$ 12.6	$ 22.0	$ 37.8
Net change in unrealized gains and losses on cash flow hedges tax expense (benefit)	6.0	(1.0)	5.4	2.3
Net change in unrealized gains and losses on available-for-sale investments net of tax benefit	$ 0.1	$ 0.0	$ (0.5)	$ 0.0