Acquisition and Investments Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Oct. 11, 2016	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Oct. 10, 2016
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments				$ (92.1)
MillerCoors
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 12,000.0
Business Acquisition, Percentage of Voting Interests Acquired						50.00%
Finite-Lived Intangible Assets, Purchase Accounting Adjustments		$ 70.0
Goodwill, Purchase Accounting Adjustments				(92.1)
Net sales			$ 2,944.6		$ 8,515.2
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax			318.9		885.6
Business Acquisition, Pro Forma Net Income (Loss)			$ 318.9		$ 883.3
Basic net income (loss) attributable to Molson Coors Brewing Company per share			$ 1.48		$ 4.12
Diluted net income (loss) attributable to Molson Coors Brewing Company per share			$ 1.47		$ 4.10
Marketing, General and Administrative Expenses [Member] | MillerCoors
Business Acquisition [Line Items]
Business Acquisition, Other Transaction Costs			$ 17.2		$ 51.7
Interest Income [Member] | MillerCoors
Business Acquisition [Line Items]
Interest Income, Deposits with Financial Institutions			(10.6)		(17.0)
Bridge Loan | Other income (expense), net [Member] | MillerCoors
Business Acquisition [Line Items]
Amortization of Debt Issuance Costs			(24.8)		(63.4)
MillerCoors Acquisition Term Loan [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Line of Credit Facility, Commitment Fee Amount			1.3		3.8
Foreign currency forwards [Member]
Business Acquisition [Line Items]
Unrealized Gain (Loss) on Derivatives			13.8		2.2
Swaption [Member] | Interest Expense [Member]
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net					36.4
Swaption [Member] | Interest Expense [Member] | MillerCoors
Business Acquisition [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net			$ 0.0		$ (36.4)
MillerCoors
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage			42.00%		42.00%	42.00%
UNITED STATES
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments				$ (92.1)