General Information - Discontinued Operations, Revenue by Service Offering (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Discontinued Operations
Total revenue	$ 184.0	$ 183.1	$ 547.4	$ 543.2
Subscription services
Discontinued Operations
Revenue	170.3	169.0	506.9	500.9
Other business services
Discontinued Operations
Revenue	5.6	5.8	16.9	17.7
Other business services - Wholesale and colocation lease revenue
Discontinued Operations
Revenue	4.8	4.9	14.6	14.6
Other revenue
Discontinued Operations
Other revenue	8.1	8.3	23.6	24.6
Residential Subscription | Subscription services
Discontinued Operations
Revenue	142.6	142.6	424.6	422.1
Residential Subscription | HSD
Discontinued Operations
Revenue	85.6	74.0	246.6	215.7
Residential Subscription | Video
Discontinued Operations
Revenue	50.0	60.1	156.1	179.0
Residential Subscription | Telephony
Discontinued Operations
Revenue	7.0	8.5	21.9	27.4
Business Subscription | Subscription services
Discontinued Operations
Revenue	27.7	26.4	82.3	78.8
Business Subscription | HSD
Discontinued Operations
Revenue	17.7	16.1	52.0	47.7
Business Subscription | Video
Discontinued Operations
Revenue	2.8	2.9	8.4	8.5
Business Subscription | Telephony
Discontinued Operations
Revenue	7.2	7.4	21.9	22.6
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale
Discontinued Operations
Other revenue	3.6		12.2
Total revenue	83.7		293.9
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Subscription services
Discontinued Operations
Revenue	79.5		280.1
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Other business services
Discontinued Operations
Revenue	0.6		1.6
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Residential Subscription
Discontinued Operations
Revenue	71.5		253.0
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Residential Subscription | HSD
Discontinued Operations
Revenue	41.4		143.5
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Residential Subscription | Video
Discontinued Operations
Revenue	27.1		98.6
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Residential Subscription | Telephony
Discontinued Operations
Revenue	3.0		10.9
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Business Subscription | Subscription services
Discontinued Operations
Revenue	8.0		27.1
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Business Subscription | HSD
Discontinued Operations
Revenue	5.0		16.7
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Business Subscription | Video
Discontinued Operations
Revenue	0.7		2.5
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale or Disposed of by Sale | Business Subscription | Telephony
Discontinued Operations
Revenue	$ 2.3		$ 7.9
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale
Discontinued Operations
Other revenue		4.6		13.4
Total revenue		105.6		312.0
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Subscription services
Discontinued Operations
Revenue		100.5		297.1
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Other business services
Discontinued Operations
Revenue		0.5		1.5
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Residential Subscription
Discontinued Operations
Revenue		91.0		268.7
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Residential Subscription | HSD
Discontinued Operations
Revenue		46.8		136.3
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Residential Subscription | Video
Discontinued Operations
Revenue		40.0		119.6
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Residential Subscription | Telephony
Discontinued Operations
Revenue		4.2		12.8
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Business Subscription | Subscription services
Discontinued Operations
Revenue		9.5		28.4
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Business Subscription | HSD
Discontinued Operations
Revenue		5.7		16.8
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Business Subscription | Video
Discontinued Operations
Revenue		0.9		2.7
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale | Business Subscription | Telephony
Discontinued Operations
Revenue		$ 2.9		$ 8.9