Investments (Schedules) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Investment [Line Items]
Equity	$ 3,827.3		$ 3,947.0
Fair value	1,187.1		1,174.8
Total	5,014.4		5,121.8
Share of results of affiliates, net	(70.9)	$ (36.5)
VodafoneZiggo JV
Investment [Line Items]
Equity	3,624.1		3,761.5
Share of results of affiliates, net	(62.3)	(26.8)
Summarized results of operations of the VodafoneZiggo JV
Revenue	1,093.9	1,196.6
Loss before income taxes	(188.8)	(103.7)
Net loss	(150.3)	(76.2)
Other
Investment [Line Items]
Equity	203.2		185.5
Fair value	310.7		298.2
Share of results of affiliates, net	(8.6)	$ (9.7)
ITV plc (ITV) — subject to re-use rights
Investment [Line Items]
Fair value	658.1		634.2
ITI Neovision S.A. (ITI Neovision)
Investment [Line Items]
Fair value	118.1		125.4
Lions Gate Entertainment Corp (Lionsgate)
Investment [Line Items]
Fair value	76.9		77.5
Casa Systems, Inc. (Casa)
Investment [Line Items]
Fair value	$ 23.3		$ 39.5

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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