Acquisition and Investments Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended			6 Months Ended
	Jul. 19, 2017	Oct. 11, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Oct. 10, 2016
Business Acquisition [Line Items]
Amortization of Debt Issuance Costs	$ 0.7		$ 0.9			$ 4.6
MillerCoors
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 12,000.0
Net sales					$ 3,109.2		$ 5,570.6
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax					309.3		566.7
Business Acquisition, Pro Forma Net Income (Loss)					$ 307.5		$ 564.4
Basic net income (loss) attributable to Molson Coors Brewing Company per share					$ 1.44		$ 2.64
Diluted net income (loss) attributable to Molson Coors Brewing Company per share					$ 1.43		$ 2.62
Business Acquisition, Percentage of Voting Interests Acquired								50.00%
Finite-Lived Intangible Assets, Purchase Accounting Adjustments				$ 70.0
Marketing, General and Administrative Expenses [Member] | MillerCoors
Business Acquisition [Line Items]
Business Acquisition, Other Transaction Costs					$ 19.6		$ 34.5
Interest Income [Member] | MillerCoors
Business Acquisition [Line Items]
Interest Income, Deposits with Financial Institutions					(3.9)		(6.4)
Bridge Loan | Other income (expense), net [Member] | MillerCoors
Business Acquisition [Line Items]
Amortization of Debt Issuance Costs					20.2		38.6
MillerCoors Acquisition Term Loan [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Line of Credit Facility, Commitment Fee Amount					1.3		2.5
Foreign currency forwards [Member]
Business Acquisition [Line Items]
Unrealized Gain (Loss) on Derivatives					11.6		11.6
Swaption [Member] | Interest Expense [Member]
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net					15.3		36.4
Swaption [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net					$ (15.3)		$ (36.4)
MillerCoors
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage					42.00%		42.00%	42.00%