v3.10.0.1

Investments (Schedules) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Investment [Line Items]
Equity	$ 4,153.7		$ 4,153.7		$ 4,324.6
Fair value	2,164.1		2,164.1		2,315.3
Cost	0.0		0.0
Cost					31.5
Total	6,317.8		6,317.8		6,671.4
Share of losses of affiliates, net	(82.3)	$ (3.6)	(118.8)	$ (19.3)
VodafoneZiggo JV
Investment [Line Items]
Equity	3,993.0		3,993.0		4,162.8
Share of losses of affiliates, net	(63.2)	6.5	(90.0)	5.2
Summarized results of operations of the VodafoneZiggo JV
Revenue	1,114.5	1,081.3	2,296.1	2,165.2
Loss before income taxes	(201.2)	(25.8)	(319.8)	(69.1)
Net loss	(150.8)	(18.3)	(238.1)	(48.6)
Other
Investment [Line Items]
Equity	160.7		160.7		161.8
Fair value	292.3		292.3		244.7
Share of losses of affiliates, net	(19.1)	$ (10.1)	(28.8)	$ (24.5)
ITV plc (ITV) — subject to re-use rights
Investment [Line Items]
Fair value	914.9		914.9		892.0
Sumitomo Corporation (Sumitomo)
Investment [Line Items]
Fair value	600.0		600.0		776.5
ITI Neovision S.A.
Investment [Line Items]
Fair value	163.8		163.8		161.9
Lions Gate Entertainment Corp (Lionsgate)
Investment [Line Items]
Fair value	120.7		120.7		163.9
Casa Systems, Inc. (Casa)
Investment [Line Items]
Fair value	$ 72.4		$ 72.4		$ 76.3

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