Quarterly Financial Information (Unaudited) New Accounting Policy (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information [Line Items]
Cost of goods sold	$ (1,514.7)	$ (1,584.1)	$ (1,750.7)	$ (1,367.7)	$ (1,481.9)	$ (537.4)	$ (558.1)	$ (410.1)	$ (6,217.2)	$ (2,987.5)	$ (2,131.6)
Marketing, general and administrative expenses									(3,032.4)	(1,589.8)	(1,038.3)
Special items, net									(28.1)	2,522.4	(346.7)
Income tax benefit (expense)									53.2	(1,055.2)	(61.5)
Net income (loss) from continuing operations attributable to MCBC									1,434.9	2,001.7	394.6
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
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.73	$ 1.33	$ 1.52	$ 0.97	$ 6.70	$ 0.97	$ 0.84	$ 0.83	$ 6.56	$ 9.41	$ 2.11
Basic net income per share (in dollars per share)	2.73	1.33	1.53	0.97	6.70	0.97	0.83	0.83	6.57	9.40	2.13
From continuing operations (in dollars per share)	2.72	1.33	1.52	0.97	6.65	0.96	0.83	0.82	6.52	9.35	2.10
Diluted net income per share (in dollars per share)	$ 2.72	$ 1.33	$ 1.52	$ 0.96	$ 6.65	$ 0.96	$ 0.82	$ 0.82	$ 6.53	$ 9.34	$ 2.12
Consolidated Statements of Comprehensive Income (Loss)
Foreign currency translation adjustments, net of tax									$ 686.7	$ (234.4)	$ (918.4)
Pension and other postretirement benefit adjustments, net of tax									145.7	53.8	19.3
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax									(3.6)	(22.8)	(16.1)
Consolidated Balance Sheets
Other assets	$ 681.5				$ 382.5				681.5	382.5
Pension and postretirement benefits	848.5				1,196.0				848.5	1,196.0
Retained earnings	7,206.1				6,145.3				7,206.1	6,145.3
Accumulated other comprehensive income (loss)	(860.0)				(1,571.8)				(860.0)	(1,571.8)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests									1,436.4	1,998.9	398.5
Income tax (benefit) expense									(53.2)	1,055.2	61.5
Pension expense (benefit)									(67.8)	(11.6)	(30.1)
As Reported
Quarterly Financial Information [Line Items]
Cost of goods sold	(1,520.3)	$ (1,589.6)	$ (1,756.1)	$ (1,372.9)	(1,485.6)	$ (541.3)	$ (562.2)	$ (414.0)	(6,238.9)	(3,003.1)	(2,163.5)
Marketing, general and administrative expenses	(779.4)	(782.8)	(781.2)	(702.8)	(753.9)	(278.9)	(313.6)	(250.9)	(3,046.2)	(1,597.3)	(1,051.8)
Special items, net	(3.7)	(4.1)	(16.5)	(3.8)	2,444.9	4.9	(34.5)	108.6	(28.1)	2,523.9	(346.7)
Income tax benefit (expense)	392.4	(145.3)	(123.0)	(64.6)	(993.2)	(19.6)	(21.2)	(16.7)	(59.5)	1,050.7	51.8
Net income (loss) from continuing operations attributable to MCBC	579.7	280.2	321.7	201.9	1,438.9	202.5	174.1	163.2
Net income (loss) attributable to Molson Coors Brewing Company	$ 580.4	$ 280.0	$ 323.3	$ 201.3	$ 1,438.4	$ 202.5	$ 172.3	$ 162.7	$ 1,385.0	$ 1,975.9	$ 359.5
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.69	$ 1.30	$ 1.49	$ 0.94	$ 6.70	$ 0.94	$ 0.81	$ 0.80	$ 6.42	$ 9.33	$ 1.92
Basic net income per share (in dollars per share)	2.69	1.30	1.50	0.94	6.70	0.94	0.80	0.80	6.43	9.32	1.94
From continuing operations (in dollars per share)	2.68	1.29	1.49	0.93	6.65	0.94	0.81	0.80	6.39	9.27	1.91
Diluted net income per share (in dollars per share)	$ 2.68	$ 1.29	$ 1.49	$ 0.93	$ 6.65	$ 0.94	$ 0.80	$ 0.80	$ 6.40	$ 9.26	$ 1.93
Consolidated Statements of Comprehensive Income (Loss)
Foreign currency translation adjustments, net of tax	$ 79.7	$ 214.9	$ 310.5	$ 81.6	$ (290.3)	$ (57.8)	$ (153.2)	$ 266.9
Pension and other postretirement benefit adjustments, net of tax	161.2	0.0	0.0	0.0	62.3	0.0	0.0	0.0	$ 161.2	$ 62.3	$ 33.6
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax	2.3	6.7	6.7	1.6	10.5	6.9	7.0	7.0	17.3	31.4	37.5
Consolidated Balance Sheets
Other assets	681.5	508.4	453.6	426.1	382.5	272.8	282.8	264.1	681.5	382.5
Pension and postretirement benefits	848.5	895.5	1,124.8	1,157.9	1,196.0	206.1	209.1	208.9	848.5	1,196.0
Retained earnings	7,150.6	6,658.7	6,467.0	6,232.0	6,119.0	4,768.9	4,654.5	4,570.4	7,150.6	6,119.0
Accumulated other comprehensive income (loss)	(804.5)	(1,038.6)	(1,222.3)	(1,470.2)	(1,545.5)	(1,633.3)	(1,573.9)	(1,437.9)	(804.5)	(1,545.5)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests	1,407.2	822.3	536.2	207.8	1,981.8	541.2	337.4	163.5	1,407.2	1,981.8	362.8
Income tax (benefit) expense	(59.5)	332.9	187.6	64.6	1,050.7	57.5	37.9	16.7	(59.5)	1,050.7	51.8
Pension expense (benefit)	(32.3)	(20.5)	(14.1)	(7.8)	10.0	6.4	4.0	2.0	(32.3)	10.0	15.3
As Adjusted
Quarterly Financial Information [Line Items]
Cost of goods sold	(1,514.7)	(1,584.1)	(1,750.7)	(1,367.7)	(1,481.9)	(537.4)	(558.1)	(410.1)	(6,217.2)	(2,987.5)	(2,131.6)
Marketing, general and administrative expenses	(775.9)	(779.2)	(777.8)	(699.5)	(752.1)	(277.1)	(311.6)	(249.0)	(3,032.4)	(1,589.8)	(1,038.3)
Special items, net	(3.7)	(4.1)	(16.5)	(3.8)	2,443.4	4.9	(34.5)	108.6	(28.1)	2,522.4	(346.7)
Income tax benefit (expense)	391.7	(147.4)	(125.2)	(65.9)	(996.3)	(20.1)	(21.7)	(17.1)	(53.2)	1,055.2	61.5
Net income (loss) from continuing operations attributable to MCBC	588.1	287.2	328.3	209.1	1,439.8	207.7	179.7	168.6
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
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.73	$ 1.33	$ 1.52	$ 0.97	$ 6.70	$ 0.97	$ 0.84	$ 0.83	$ 6.56	$ 9.41	$ 2.11
Basic net income per share (in dollars per share)	2.73	1.33	1.53	0.97	6.70	0.97	0.83	0.83	6.57	9.40	2.13
From continuing operations (in dollars per share)	2.72	1.33	1.52	0.97	6.65	0.96	0.83	0.82	6.52	9.35	2.10
Diluted net income per share (in dollars per share)	$ 2.72	$ 1.33	$ 1.52	$ 0.96	$ 6.65	$ 0.96	$ 0.82	$ 0.82	$ 6.53	$ 9.34	$ 2.12
Consolidated Statements of Comprehensive Income (Loss)
Foreign currency translation adjustments, net of tax	$ 79.0	$ 215.2	$ 310.9	$ 81.6	$ (290.0)	$ (57.8)	$ (153.5)	$ 266.9
Pension and other postretirement benefit adjustments, net of tax	145.7	0.0	0.0	0.0	53.8	0.0	0.0	0.0	$ 145.7	$ 53.8	$ 19.3
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax	(4.7)	4.6	4.7	(1.0)	10.0	4.2	4.3	4.3	3.6	22.8	16.1
Consolidated Balance Sheets
Other assets	681.5	522.3	462.6	430.4	382.5	278.7	286.8	266.2	681.5	382.5
Pension and postretirement benefits	848.5	894.6	1,124.2	1,157.6	1,196.0	204.2	207.8	208.3	848.5	1,196.0
Retained earnings	7,206.1	6,705.8	6,507.1	6,265.5	6,145.3	4,794.3	4,674.7	4,585.0	7,206.1	6,145.3
Accumulated other comprehensive income (loss)	(860.0)	(1,070.9)	(1,252.8)	(1,499.1)	(1,571.8)	(1,650.9)	(1,588.8)	(1,449.8)	(860.0)	(1,571.8)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests	1,436.4	843.1	550.0	215.0	1,998.9	557.4	348.4	168.9	1,436.4	1,998.9	398.5
Income tax (benefit) expense	(53.2)	338.5	191.1	65.9	1,055.2	58.9	38.8	17.1	(53.2)	1,055.2	61.5
Pension expense (benefit)	$ (67.8)	$ (46.9)	$ (31.4)	$ (16.3)	$ (11.6)	$ (11.2)	$ (7.9)	$ (3.8)	$ (67.8)	$ (11.6)	$ (30.1)