Income Taxes - Summary of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019
Deferred tax assets:
Pensions	$ 96.7	$ 86.9
Postretirement provisions	39.1	35.7
Net operating loss carryforwards	28.1	28.8
Operating lease liability	14.7	0.0
Other	34.8	36.2
Gross deferred tax assets	213.4	187.6
Valuation allowances	(24.2)	(24.6)
Total deferred tax assets	189.2	163.0
Deferred tax liabilities:
Depreciation	(257.7)	(249.5)
Intangible assets	(5.2)	(11.3)
Inventories	(33.9)	(36.1)
Operating lease right-of-use asset	(12.6)	0.0
Other	(5.1)	(4.6)
Total deferred tax liabilities	(314.5)	(301.5)
Deferred tax liabilities, net	$ (125.3)	$ (138.5)