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Business Combinations (Details) $ in Millions, $ in Millions					1 Months Ended		3 Months Ended			9 Months Ended
	Jun. 01, 2018 USD ($)	May 23, 2018 USD ($)	May 23, 2018 CAD ($)	Apr. 03, 2017 USD ($)	May 31, 2019 USD ($)	May 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2016 USD ($) pharmacy	Dec. 31, 2016 CAD ($) pharmacy	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill										$ 9,456		$ 9,358
Net purchase consideration										97	$ 866
Medical Specialties Distributors LLC (“MSD”)
Business Acquisition [Line Items]
Consideration transferred to acquire business	$ 784
Assets acquired as of the acquisition date, excluding goodwill and intangibles							$ 239
Liabilities assumed as of the acquisition date							169
Goodwill							388
Intangible assets							$ 326
Weighted average life of intangibles							18 years
CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Net purchase consideration				$ 1,300
Rexall Health | Canada
Business Acquisition [Line Items]
Net purchase consideration								$ 2,100	$ 2,900
Number of retail pharmacies | pharmacy								400	400
Estimate of Fair Value | CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Payment for contingent consideration liability					$ 69	$ 68
Contingent consideration										$ 0		$ 69
Third Party Seller of Rexall Health | Rexall Health | Canada
Business Acquisition [Line Items]
Proceeds from prior acquisitions		$ 97	$ 125								$ 97

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