Fair Value Measurements - Narrative (Details) $ in Millions	Jun. 30, 2018 USD ($)	Mar. 31, 2018 interest_rate_swap	Sep. 30, 2017 USD ($)	Mar. 31, 2017 interest_rate_swap
Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Number of new swaps entered into to manage interest rate exposure | interest_rate_swap		3		4
Level 2 | Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Number of new swaps entered into to manage interest rate exposure | interest_rate_swap				4
Level 2 | Cash Flow Hedging | Interest Rate Swap | Other current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative asset	$ 1.6		$ 0.0
Level 2 | Cash Flow Hedging | Interest Rate Swap | Other non-current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative asset	6.7		0.3
Level 2 | Cash Flow Hedging | Interest Rate Swap | Accrued expenses and other liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative liability	0.4		1.1
Level 2 | Cash Flow Hedging | Interest Rate Swap | Other non-current liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Derivative liability	0.0		0.2
TRA Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Estimated adjustment to contingent consideration liability discount rate	0.1
Estimated adjustment to contingent consideration liability tax rate	2.3
Nexeo Solutions Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration - Fair value of deferred cash consideration	46.3		35.1
Contingent consideration - Fair value of TRA	$ 75.0		$ 105.1