Organization and Basis of Presentation - Discontinued Operations, Components of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other income (expense):
Income from discontinued operations, net of tax	$ 839.1	$ 122.7	$ 118.8
Atlantic and Astound broadband markets | Discontinued Operations, Disposed of by sale
Discontinued operations - Components of income
Revenue	308.3
Costs and expenses
Operating (excluding depreciation and amortization)	112.0
Selling, general and administrative	11.8
Depreciation and amortization	41.0
Total costs and expenses	164.8
Income from operations	143.5
Other income (expense):
Interest income (expense)	0.4
Gain on sale of assets, net	1,001.8
Other income, net	0.1
Income from discontinued operations before provision for income tax	1,145.8
Income tax expense	(306.7)
Income from discontinued operations, net of tax	$ 839.1
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale
Discontinued operations - Components of income
Revenue		418.2	418.8
Costs and expenses
Operating (excluding depreciation and amortization)		165.0	178.4
Selling, general and administrative		12.3	13.0
Depreciation and amortization		79.6	72.8
Total costs and expenses		256.9	264.2
Income from operations		161.3	154.6
Other income (expense):
Interest income (expense)		(0.7)	(0.2)
Other income, net		0.5	(0.2)
Income from discontinued operations before provision for income tax		161.1	154.2
Income tax expense		(38.4)	(35.4)
Income from discontinued operations, net of tax		$ 122.7	$ 118.8