Discontinued Operations - Components of Income (Details) $ in Millions		3 Months Ended	6 Months Ended
	Jun. 30, 2021 agreement Counterparty	Jun. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)
Discontinued Operations
Number of separate asset sales | agreement	2
Number of different buyers in asset sales | Counterparty	2
Other income (expense):
Income from discontinued operations		$ 34.9	$ 67.2
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale
Discontinued operations - Components of income
Revenue		105.4	210.2
Costs and expenses
Operating (excluding depreciation and amortization)		37.6	77.2
Selling, general and administrative		2.8	5.5
Depreciation and amortization		20.5	41.0
Total costs and expenses		60.9	123.7
Income from operations		44.5	86.5
Other income (expense):
Interest income (expense)		0.4	0.4
Gain on sale of assets, net		0.2	0.2
Other income, net		0.1	0.1
Income from discontinued operations before provision for income tax		45.2	87.2
Income tax expense		(10.3)	(20.0)
Income from discontinued operations		$ 34.9	$ 67.2