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Special Items Special Items Recorded By Segment (Narrative) (Details) $ in Millions, $ in Millions		3 Months Ended	12 Months Ended
	Jan. 21, 2018 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 CAD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				$ 674.4
Accelerated depreciation				31.7	$ 30.7	$ 20.5
Special items, net				708.8	(249.7)	36.4
Canada
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss		$ 668.3		668.3	0.0	0.0
Canada \| Sale of Asset [Member]
Unusual or Infrequent Item [Line Items]
Unusual or Infrequent Item, or Both, Gain, Gross				61.3	0.0	0.0
Canada \| Asset Abandonment [Member]
Unusual or Infrequent Item [Line Items]
Special items, net				23.0	24.5	14.4
Europe [Member]
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				0.0
Europe [Member] \| Sale of Asset [Member]
Unusual or Infrequent Item [Line Items]
Unusual or Infrequent Item, or Both, Gain, Gross				0.0	0.0	4.6
Europe [Member] \| Asset Abandonment [Member]
Unusual or Infrequent Item [Line Items]
Special items, net				1.2	3.8	9.5
International
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				6.1
Impairment of finite-lived intangible assets				6.1
U.S.
Unusual or Infrequent Item [Line Items]
Goodwill, Impairment Loss				0.0
U.S. \| Sale of Asset [Member]
Unusual or Infrequent Item [Line Items]
Unusual or Infrequent Item, or Both, Gain, Gross				7.5	0.0	0.0
U.S. \| Asset Abandonment [Member]
Unusual or Infrequent Item [Line Items]
Special items, net				15.8	$ 8.2	14.5
Irwindale Brewery [Member]
Unusual or Infrequent Item [Line Items]
Agreement Purchase Price				150.0
Montreal Brewery [Member] \| Estimated future charges [Member]
Unusual or Infrequent Item [Line Items]
Accelerated depreciation			$ 27
Plovdiv Brewery [Member] \| Europe [Member]
Unusual or Infrequent Item [Line Items]
Gain (Loss) on Disposition of Assets						4.6
Plovdiv Brewery [Member] \| Europe [Member] \| Cash proceeds [Member]
Unusual or Infrequent Item [Line Items]
Accounts and Other Receivables, Net, Current						$ 8.2
Minimum \| Irwindale Brewery [Member] \| Estimated future charges [Member]
Unusual or Infrequent Item [Line Items]
Accelerated depreciation				150.0
Maximum \| Irwindale Brewery [Member] \| Estimated future charges [Member]
Unusual or Infrequent Item [Line Items]
Accelerated depreciation				$ 175.0
Millercoors [Member]
Unusual or Infrequent Item [Line Items]
CashReceivedforAdjustmentAmount	$ 330.0
AdjustmentAmount	$ 328.0