Income Taxes - Summary of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020
Deferred tax assets:
Pensions	$ 51.5	$ 96.7
Postretirement provisions	30.5	39.1
Net operating loss carryforwards	38.7	28.1
Tax credit carryforwards	26.0	0.6
Operating lease liability	8.9	14.7
Other	38.7	34.2
Gross deferred tax assets	194.3	213.4
Valuation allowances	(25.2)	(24.2)
Total deferred tax assets	169.1	189.2
Deferred tax liabilities:
Depreciation	(271.3)	(257.7)
Intangible assets	(6.1)	(5.2)
Inventories	(30.6)	(33.9)
Operating lease right-of-use asset	(6.6)	(12.6)
Other	(6.0)	(5.1)
Total deferred tax liabilities	(320.6)	(314.5)
Deferred tax liabilities, net	$ (151.5)	$ (125.3)