Stockholders' Deficit Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (58.4)	$ (63.5)
Net unrealized gains on securities classified as available-for-sale, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	1.2	1.6	$ 1.9	$ 2.2
Cumulative non-U.S. dollar translation adjustments, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(20.9)	(28.1)	(24.2)	(10.4)
Pension and postretirement benefits adjustments, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (38.7)	$ (37.0)	$ (45.2)	$ (54.8)