Acquisition and Investments Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Oct. 11, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Oct. 10, 2016
Business Acquisition [Line Items]
Amortization of Debt Issuance Costs		$ 3.7
MillerCoors
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 12,000.0
Net sales				$ 2,461.4
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax				257.4
Business Acquisition, Pro Forma Net Income (Loss)				$ 256.9
Basic net income (loss) attributable to Molson Coors Brewing Company per share				$ 1.20
Diluted net income (loss) attributable to Molson Coors Brewing Company per share				$ 1.19
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				$ 14.9
Interest Income [Member] | MillerCoors
Business Acquisition [Line Items]
Interest Income, Deposits with Financial Institutions				(2.5)
Bridge Loan | Other income (expense), net [Member] | MillerCoors
Business Acquisition [Line Items]
Amortization of Debt Issuance Costs				18.4
MillerCoors Acquisition Term Loan [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Line of Credit Facility, Commitment Fee Amount				1.2
Swaption [Member] | Interest Expense [Member]
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				21.1
Swaption [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				$ 21.1
MillerCoors
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage				42.00%	42.00%