Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Operating losses	$ 63.2	$ 68.4
Interest expense carryforward	93.5	62.3
Restructuring costs	2.3	3.9
Bad debts	4.9	3.9
Accrued expenses	9.0	21.0
Capital loss and credit carryforwards	13.8	11.5
Foreign exchange	0.0	2.4
Pension and postretirement benefits	71.2	49.9
ASC 842 - Lease liability	17.6	17.1
Other	9.0	5.0
Total deferred tax assets	284.5	245.4
Valuation allowance	(35.8)	(33.1)
Net deferred tax assets	248.7	212.3
Deferred tax liabilities:
Intangibles	(1,318.2)	(1,408.3)
Foreign exchange	(6.3)	0.0
Deferred revenue	0.0	(4.1)
ASC 842 - ROU asset	(15.2)	(20.5)
Other	0.0	(0.3)
Total deferred tax liabilities	(1,339.7)	(1,433.2)
Net deferred tax (liabilities) assets	$ (1,091.0)	$ (1,220.9)