Special Items Schedule of Special Items Recorded By Segment (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended					12 Months Ended
	Jan. 21, 2018	Jun. 30, 2019	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Special items, net								$ 1,740.2	$ 708.8	$ (249.7)
Goodwill, Impairment Loss								1,484.3	674.4
Millercoors [Member]
Restructuring Cost and Reserve [Line Items]
CashReceivedforAdjustmentAmount	$ 330.0
AdjustmentAmount	$ 328.0
Other Employee-Related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								67.6	52.4	34.7
Acquisition purchase price adjustment settlement gain [Member]
Restructuring Cost and Reserve [Line Items]
Unusual or Infrequent Item, or Both, Gain, Gross							$ (328.0)
Sale of Montreal Brewery
Restructuring Cost and Reserve [Line Items]
Proceeds from Sale of Property, Plant, and Equipment		$ 96.2
Sale and Leaseback Transaction, Gain (Loss), Net		$ 61.3
International
Restructuring Cost and Reserve [Line Items]
Goodwill, Impairment Loss					$ 6.1
Impairment of finite-lived intangible assets					6.1
Irwindale Brewery [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								117.7	15.8
North America [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Impairment Loss					$ 668.3			0.0	668.3
North America [Member] | Asset Abandonment [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								115.8	38.8	32.7
North America [Member] | Impairment Losses [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								39.6	671.7	0.0
North America [Member] | Termination fees and other [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net									(68.3)	(326.9)
North America [Member] | Irwindale Brewery [Member] | Termination fees and other [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								(2.0)
Europe [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Impairment Loss			$ 1,484.3					1,484.3	6.1
Goodwill and Intangible Asset Impairment									12.2
Europe [Member] | Asset Abandonment [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								3.7	1.2	3.8
Europe [Member] | Impairment Losses [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net				$ 30.0				1,516.2	12.2	0.0
Europe [Member] | Termination fees and other [Member]
Restructuring Cost and Reserve [Line Items]
Special items, net								$ (0.7)	$ 0.8	$ 6.0
Canada | Sale of Montreal Brewery
Restructuring Cost and Reserve [Line Items]
Proceeds from Sale of Property, Plant, and Equipment						$ 96.2
Sale and Leaseback Transaction, Gain (Loss), Net						$ 61.3