Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Cost of Goods Sold	$ (1,714.0)		$ (1,589.1)			$ (4,988.8)	$ (4,716.9)
Capital Expenditures Incurred but Not yet Paid						169.7	153.8
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent			(0.2)				0.8
Selling, General and Administrative Expense	(713.9)		(783.8)			(2,139.7)	(2,271.5)
Special items, net	(36.6)		(4.1)			267.7	(27.3)
Income tax benefit (expense)	(64.5)		(147.4)			(231.6)	(338.5)
Net income (loss) attributable to Molson Coors Brewing Company	$ 338.3		287.0			$ 1,040.5	$ 825.4
Restatement Adjustment [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Cost of Goods Sold		$ (1,514.7)	(1,584.1)	$ (1,750.7)	$ (1,367.7)
Selling, General and Administrative Expense		(775.9)	(779.2)	(777.8)	(699.5)
Special items, net		(3.7)	(4.1)	(16.5)	(3.8)
Income tax benefit (expense)		391.7	(147.4)	(125.2)	(65.9)
Net income (loss) attributable to Molson Coors Brewing Company		$ 588.8	$ 287.0	$ 329.9	$ 208.5
Earnings Per Share, Basic		$ 2.73	$ 1.33	$ 1.53	$ 0.97
Earnings Per Share, Diluted		$ 2.72	$ 1.33	$ 1.52	$ 0.96
Previously Reported [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Cost of Goods Sold		$ (1,520.3)	$ (1,589.6)	$ (1,756.1)	$ (1,372.9)
Selling, General and Administrative Expense		(779.4)	(782.8)	(781.2)	(702.8)
Special items, net		(3.7)	(4.1)	(16.5)	(3.8)
Income tax benefit (expense)		392.4	(145.3)	(123.0)	(64.6)
Net income (loss) attributable to Molson Coors Brewing Company		$ 580.4	$ 280.0	$ 323.3	$ 201.3
Earnings Per Share, Basic		$ 2.69	$ 1.30	$ 1.50	$ 0.94
Earnings Per Share, Diluted		$ 2.68	$ 1.29	$ 1.49	$ 0.93