Accounting Changes Accounting Changes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Oct. 01, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings, tax effect				$ (6.6)
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings, tax effect	$ 6.6
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net periodic defined benefits expense (reversal of expense), excluding service cost component		$ 0.2	$ (1.5)	$ 0.3	$ (4.7)