Income Taxes - Summary of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jun. 30, 2017
Deferred tax assets:
Pensions	$ 66.8	$ 139.8
Postretirement provisions	33.7	54.4
Net operating loss carryforwards	26.5	23.1
Derivatives and hedging activities	0.0	2.4
Other	29.4	44.8
Gross deferred tax assets	156.4	264.5
Valuation allowances	(23.9)	(18.5)
Total deferred tax assets	132.5	246.0
Deferred tax liabilities:
Depreciation	(235.2)	(347.5)
Intangible assets	(11.9)	(19.4)
Inventories	(30.5)	(50.1)
Derivatives and hedging activities	(8.7)	0.0
Other	(3.5)	(6.2)
Total deferred tax liabilities	(289.8)	(423.2)
Deferred tax liabilities, net	$ (157.3)	$ (177.2)