Merger Agreement - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions					12 Months Ended
	Feb. 14, 2019	Oct. 02, 2018	Aug. 09, 2018	Jun. 10, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Common stock - par value (in dollars per share)					$ 0.1	$ 0.1
Conditional special dividend, additional amount paid to holders of stock options					$ 2
Knauf And World Cup Acquisition Corporation
Business Acquisition [Line Items]
Common stock - par value (in dollars per share)				$ 0.10
Conversion price (in dollars per share)				$ 43.50
Special cash dividend (in dollars per share)			$ 0.50
Conditional special dividend, amount		$ 70
Merger related costs					$ 19
Scenario, Forecast | Knauf And World Cup Acquisition Corporation
Business Acquisition [Line Items]
Conversion price (in dollars per share)	$ 43.50
Termination fee, contingency of merger agreement	$ 215