Investments (Narrative) (Details) $ / shares in Units, € in Millions			3 Months Ended								12 Months Ended
	Dec. 31, 2016	Nov. 12, 2015 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2018 EUR (€) shares	Dec. 31, 2018 USD ($) shares	Oct. 31, 2018	Jan. 04, 2017
Schedule of Investments [Line Items]
Value-added taxes (VAT) paid on behalf of the VodafoneZiggo JV											$ 0	$ 162,600,000	$ 0
Distributions received from affiliates											0	1,569,400,000	0
Revenue			$ 2,949,100,000	$ 2,929,700,000	$ 3,015,600,000	$ 3,063,500,000	$ 2,987,800,000	$ 2,899,300,000	$ 2,746,800,000	$ 2,642,500,000	$ 11,957,900,000	$ 11,276,400,000	13,731,100,000
VodafoneZiggo JV
Schedule of Investments [Line Items]
Percent of interest income earned														100.00%	100.00%
Percent of share-based compensation included														100.00%	100.00%
Ownership percentage							50.00%					50.00%		50.00%	50.00%		50.00%
Co-venturer ownership percentage														50.00%	50.00%
Term to distribute all unrestricted cash											2 months
Value-added taxes (VAT) paid on behalf of the VodafoneZiggo JV										$ 162,600,000
Distributions received from affiliates											$ 232,500,000	$ 252,800,000
Revenue													$ 0
VodafoneZiggo JV | Minimum
Schedule of Investments [Line Items]
Leverage ratio														4.5	4.5
Continuing and required services term	4 years
VodafoneZiggo JV | Maximum
Schedule of Investments [Line Items]
Leverage ratio														5.0	5.0
VodafoneZiggo JV | Equity Method Investee
Schedule of Investments [Line Items]
Payments to Acquire Equity Method Investments											$ 13,100,000	144,700,000
Due from related parties							$ 33,300,000					33,300,000			$ 24,400,000
VodafoneZiggo JV | VodafoneZiggo JV Loan
Schedule of Investments [Line Items]
Related party note receivable							$ 1,081,900,000					1,081,900,000			916,100,000
Related party note receivable rate											5.55%
Related party note receivable in year one														€ 100.0	114,500,000
Related party note receivable in year two														100.0	114,500,000
Related party note receivable in year three														€ 100.0	$ 114,500,000
Interest accrued on receivable											$ 59,600,000
All3Media
Schedule of Investments [Line Items]
Ownership percentage														50.00%	50.00%
JV Services
Schedule of Investments [Line Items]
Revenue											$ 189,100,000	$ 132,400,000
ITV
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares							398,515,510					398,515,510		398,515,510	398,515,510
Percent of investment owned (less than 5% for Sumitomo and Lionsgate)					10.00%
Sumitomo Corporation (Sumitomo)
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares							45,652,175					45,652,175
Percent of investment owned (less than 5% for Sumitomo and Lionsgate)							5.00%					5.00%
ITI Neovision S.A. (ITI Neovision)
Schedule of Investments [Line Items]
Percent of investment owned (less than 5% for Sumitomo and Lionsgate)							17.00%					17.00%		17.00%	17.00%
Lions Gate Entertainment Corp (Lionsgate)
Schedule of Investments [Line Items]
Percent of investment owned (less than 5% for Sumitomo and Lionsgate)														5.00%	5.00%
Share price (in dollars per share) | $ / shares		$ 39.02
Investment owned		$ 195,100,000
Lions Gate Entertainment Corp (Lionsgate) | Lionsgate Forward
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares		1,250,000
Proceeds from derivative instrument		$ 70,900,000
Lions Gate Entertainment Corp (Lionsgate) | Common Stock
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares														2,500,000	2,500,000
Lions Gate Entertainment Corp (Lionsgate) | Nonvoting Common Stock
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares														2,500,000	2,500,000
Casa Systems, Inc. (Casa)
Schedule of Investments [Line Items]
Number of common stock shares owned (in shares) | shares							4,432,870					4,432,870		3,005,307	3,005,307
Percent of investment owned (less than 5% for Sumitomo and Lionsgate)																5.50%