Special Items Special Items Recorded By Segment (Narrative) (Details) $ in Millions, $ in Millions		3 Months Ended			12 Months Ended
	Jan. 21, 2018 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 CAD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss					$ 1,484.3		$ 674.4
Accelerated depreciation					112.3		31.7	$ 30.7
Special items, net					1,740.2		708.8	(249.7)
North America [Member]
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				$ 668.3	0.0		668.3
Europe [Member]
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss		$ 1,484.3			1,484.3		6.1
Other Employee-Related Costs [Member]
Unusual or Infrequent Item [Line Items]
Special items, net					67.6		52.4	34.7
Asset Abandonment [Member] | North America [Member]
Unusual or Infrequent Item [Line Items]
Special items, net					115.8		38.8	32.7
Asset Abandonment [Member] | Europe [Member]
Unusual or Infrequent Item [Line Items]
Special items, net					3.7		1.2	3.8
Revitalization Restructuring Costs [Member]
Unusual or Infrequent Item [Line Items]
Restructuring Charges					35.6		41.2
Impairment Losses [Member] | North America [Member]
Unusual or Infrequent Item [Line Items]
Special items, net					39.6		671.7	0.0
Impairment Losses [Member] | Europe [Member]
Unusual or Infrequent Item [Line Items]
Special items, net			$ 30.0		1,516.2		12.2	$ 0.0
Grolsch [Member]
Unusual or Infrequent Item [Line Items]
Unusual or Infrequent Item, Loss, Gross							0.5
Craft Brand Definite-Lived Intangible Asset Impairment Losses [Member] | North America [Member]
Unusual or Infrequent Item [Line Items]
Special items, net		17.0
Definite-Lived Intangible Asset Impairment Losses [Member] | North America [Member]
Unusual or Infrequent Item [Line Items]
Special items, net		$ 22.6
International
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				6.1
Impairment of finite-lived intangible assets				$ 6.1
Corporate | Closure of Denver Office [Member]
Unusual or Infrequent Item [Line Items]
Special items, net					7.6		2.1
Irwindale Brewery [Member]
Unusual or Infrequent Item [Line Items]
Agreement Purchase Price					150.0
Accelerated depreciation					96.0		8.0
Special items, net					117.7		15.8
Gain (Loss) on Disposition of Other Assets					2.1
Irwindale Brewery [Member] | Other Employee-Related Costs [Member]
Unusual or Infrequent Item [Line Items]
Restructuring Charges					16.5		$ 1.1
Montreal Brewery [Member] | Estimated future charges [Member]
Unusual or Infrequent Item [Line Items]
Accelerated depreciation						$ 10
Employee Relocation [Member]
Unusual or Infrequent Item [Line Items]
Restructuring Costs					$ 11.0
Millercoors [Member]
Unusual or Infrequent Item [Line Items]
CashReceivedforAdjustmentAmount	$ 330.0
AdjustmentAmount	$ 328.0