Income Taxes - Detail of Deferred Tax Assets and Liabilities (Details 2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating and capital loss and tax credit carryforwards	$ 496.2	$ 516.7
Postretirement benefits	87.9	81.8
Pension benefits	84.2	114.1
Leases	63.3	0.0
Inventories	23.4	38.5
Other assets	78.9	65.1
Valuation allowance	(659.4)	(693.5)	$ (735.7)	$ (1,189.7)
Total deferred tax assets	174.5	122.7
Deferred tax liabilities:
Depreciable assets	(106.3)	(108.3)
Leases	(60.0)	0.0
Other liabilities	(27.9)	(33.4)
Total deferred tax liabilities	(194.2)	(141.7)
Net deferred tax liabilities	$ (19.7)	$ (19.0)