Discontinued Operations - Reconciliation of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Loss from discontinued operations	$ 0.0	$ (2.5)	$ 0.0	$ (7.3)
T-System Holdings, Inc. | Discontinued Operations, Held-for-sale
Revenues:
Other operating revenue		13.4		38.5
Total operating revenues		13.4		38.5
Operating expenses:
Personnel costs		8.2		24.3
Depreciation and amortization		3.4		10.3
Other operating expenses		3.9		12.6
Total operating expenses		15.5		47.2
Operating loss		(2.1)		(8.7)
Recognized loss				(0.5)
Total other expense				(0.5)
Loss from discontinued operations before income taxes		(2.1)		(9.2)
Income tax expense (benefit)		0.4		(1.9)
Loss from discontinued operations		$ (2.5)		$ (7.3)