Segment Reporting (Revenue by Major Category) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Principal Transaction Revenue [Line Items]
Revenue	$ 2,949.1	$ 2,929.7	$ 3,015.6	$ 3,063.5	$ 2,987.8	$ 2,899.3	$ 2,746.8	$ 2,642.5	$ 11,957.9	$ 11,276.4	$ 13,731.1
Total residential cable revenue
Principal Transaction Revenue [Line Items]
Revenue									7,976.7	7,709.6	10,100.4
Total subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									7,697.6	7,366.0	9,788.5
Video
Principal Transaction Revenue [Line Items]
Revenue									2,863.2	2,786.5	4,060.0
Broadband internet
Principal Transaction Revenue [Line Items]
Revenue									3,226.6	2,979.7	3,579.0
Fixed-line telephony
Principal Transaction Revenue [Line Items]
Revenue									1,607.8	1,599.8	2,149.5
Non-subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									279.1	343.6	311.9
Total residential revenue
Principal Transaction Revenue [Line Items]
Revenue									9,655.0	9,316.4	11,795.1
Total residential mobile revenue
Principal Transaction Revenue [Line Items]
Revenue									1,678.3	1,606.8	1,694.7
Subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									983.5	999.7	1,103.9
Non-subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									694.8	607.1	590.8
Total B2B revenue
Principal Transaction Revenue [Line Items]
Revenue									1,983.5	1,740.1	1,854.2
Subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									446.4	367.6	366.3
Non-subscription revenue
Principal Transaction Revenue [Line Items]
Revenue									1,537.1	1,372.5	1,487.9
Other revenue
Principal Transaction Revenue [Line Items]
Revenue									$ 319.4	$ 219.9	$ 81.8