Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Accrued postretirement benefits cost	$ 72.3	$ 91.4
Accrued pension cost	36.3	16.3
Other employee benefit accruals	10.9	16.9
Tax loss and credit carryforwards	100.3	117.9
Other, net	40.0	60.0
Valuation allowances	(83.7)	(145.4)
Total deferred tax assets	176.1	157.1
Deferred tax liabilities - principally depreciation and amortization	(113.8)	(100.3)
Net deferred tax assets	$ 62.3	$ 56.8