Basis of Presentation (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 market country	Dec. 31, 2017	Dec. 31, 2016
Telenet [Member]
Basis of Presentation [Line Items]
Percentage ownership in subsidiary	57.60%
VodafoneZiggo JV [Member]
Basis of Presentation [Line Items]
Ownership percentage	50.00%	50.00%	50.00%
Liberty Puerto Rico [Member]
Basis of Presentation [Line Items]
Ownership percentage	60.00%
Video, Broadband Internet and FIxed-Line Telephony, Mobile and other Communications Services [Member] | Europe [Member]
Basis of Presentation [Line Items]
Number of countries in which entity provides services	11
Consumer and Business-to-Business Communication Services [Member] | Europe [Member]
Basis of Presentation [Line Items]
Number of countries in which entity provides services	7
Consumer and Business-to-Business Communication Services [Member] | Latin America and the Caribbean [Member]
Basis of Presentation [Line Items]
Number of countries in which entity provides services	18
Sub-Sea Networks [Member] | Cable & Wireless Communications Limited (C&W) [Member]
Basis of Presentation [Line Items]
Number of markets | market	40