Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) from continuing operations	$ 588.1	$ 287.2	$ 328.3	$ 209.1	$ 1,439.8	$ 207.7	$ 179.7	$ 168.6	$ 1,412.7	$ 1,995.8	$ 391.3
Income (loss) from discontinued operations, net of tax	0.7	(0.2)	1.6	(0.6)	(0.5)	0.0	(1.8)	(0.5)	1.5	(2.8)	3.9
Net income (loss) attributable to Molson Coors Brewing Company	$ 588.8	$ 287.0	$ 329.9	$ 208.5	$ 1,439.3	$ 207.7	$ 177.9	$ 168.1	$ 1,414.2	$ 1,993.0	$ 395.2
Weighted-average shares for basic EPS									215.4	212.0	185.3
Effect of dilutive securities:
Weighted-average shares for diluted EPS									216.5	213.4	186.4
Basic net income (loss) attributable to Molson Coors Brewing Company per share:
From continuing operations	$ 2.73	$ 1.33	$ 1.52	$ 0.97	$ 6.70	$ 0.97	$ 0.84	$ 0.83	$ 6.56	$ 9.41	$ 2.11
From discontinued operations	0.00	0.00	0.01	0.00	0.00	0.00	(0.01)	0.00	0.01	(0.01)	0.02
Basic net income (loss) attributable to Molson Coors Brewing Company per share	2.73	1.33	1.53	0.97	6.70	0.97	0.83	0.83	6.57	9.40	2.13
Diluted net income (loss) attributable to Molson Coors Brewing Company per share:
From continuing operations	2.72	1.33	1.52	0.97	6.65	0.96	0.83	0.82	6.52	9.35	2.10
From discontinued operations	0.00	0.00	0.00	(0.01)	0.00	0.00	(0.01)	0.00	0.01	(0.01)	0.02
Diluted net income (loss) attributable to Molson Coors Brewing Company per share	$ 2.72	$ 1.33	$ 1.52	$ 0.96	$ 6.65	$ 0.96	$ 0.82	$ 0.82	6.53	9.34	2.12
Dividends declared and paid per share (in dollars per share)									$ 1.64	$ 1.64	$ 1.64
RSU DSU PSU
Effect of dilutive securities:
Incremental common shares attributable to share-based compensation arrangements									0.6	0.8	0.7
Options and SOSARs
Effect of dilutive securities:
Incremental common shares attributable to share-based compensation arrangements									0.5	0.6	0.4