Segment Reporting (Revenue by Major Category) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 2,954.5	$ 2,840.9	$ 8,553.2	$ 8,559.3
Total residential cable revenue
Segment Reporting Information [Line Items]
Revenue	1,884.6	1,821.8	5,534.2	5,620.5
Total subscription revenue
Segment Reporting Information [Line Items]
Revenue	1,836.0	1,778.2	5,397.0	5,478.4
Video
Segment Reporting Information [Line Items]
Revenue	680.8	660.5
Fixed-line telephony
Segment Reporting Information [Line Items]
Revenue	332.4	341.1
Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue	48.6	43.6
Total residential revenue
Segment Reporting Information [Line Items]
Revenue	2,315.3	2,222.8	6,703.1	6,810.9
Subscription revenue
Segment Reporting Information [Line Items]
Revenue	251.1	235.0
Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue	179.6	166.0
Total residential mobile revenue
Segment Reporting Information [Line Items]
Revenue	430.7	401.0	1,168.9	1,190.4
Total B2B revenue
Segment Reporting Information [Line Items]
Revenue	501.9	463.3	1,437.6	1,423.1
Subscription revenue
Segment Reporting Information [Line Items]
Revenue	134.5	119.8
Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue	367.4	343.5
Other revenue
Segment Reporting Information [Line Items]
Revenue	137.3	154.8
Broadband internet
Segment Reporting Information [Line Items]
Revenue	$ 822.8	$ 776.6	2,400.6	2,378.9
Video | Video
Segment Reporting Information [Line Items]
Revenue			1,997.5	2,029.2
Fixed-line telephony | Fixed-line telephony
Segment Reporting Information [Line Items]
Revenue			998.9	1,070.3
Non-subscription revenue | Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue			137.2	142.1
Subscription revenue | Subscription revenue
Segment Reporting Information [Line Items]
Revenue			714.3	694.4
Non-subscription revenue | Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue			454.6	496.0
Subscription revenue | Subscription revenue
Segment Reporting Information [Line Items]
Revenue			382.5	350.4
Non-subscription revenue | Non-subscription revenue
Segment Reporting Information [Line Items]
Revenue			1,055.1	1,072.7
Other revenue | Other revenue
Segment Reporting Information [Line Items]
Revenue			$ 412.5	$ 325.3