Fair Value Measurements - (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trademarks and tradenames	$ 7.9	$ 0.0	$ 0.0
Carrying amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	4,210.9	4,211.9	4,175.3
Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 4,143.1	$ 4,346.8	$ 4,267.0
Trademarks and Trade Names
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Finite-lived intangible asset, useful life	3 years