Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2018	Oct. 25, 2018
Entity Information [Line Items]
Entity Registrant Name	MOLSON COORS BREWING CO
Trading Symbol	tap
Entity Central Index Key	0000024545
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Common Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		2,562,668
Common Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		195,644,139
Class A Exchangeable Shares [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		2,757,201
Class B Exchangeable Shares [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		14,807,312