Business Combinations (Details) CAD in Millions					9 Months Ended
	Jan. 02, 2018 USD ($)	Apr. 03, 2017 USD ($)	Dec. 28, 2016 USD ($) pharmacy	Dec. 28, 2016 CAD	Dec. 31, 2017 USD ($) pharmacy	Dec. 31, 2017 CAD pharmacy	Dec. 31, 2016 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 CAD	Mar. 31, 2017 USD ($)
Business Acquisition [Line Items]
Net purchase consideration					$ 1,979,000,000		$ 4,174,000,000
Goodwill					11,828,000,000					$ 10,586,000,000
Gain (loss) on sale of stores					155,000,000		(113,000,000)
CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Net purchase consideration		$ 1,300,000,000
Assets acquired as of the acquisition date, excluding goodwill and intangibles		52,000,000
Liabilities assumed as of the acquisition date		7,000,000
Goodwill		870,000,000
Acquired identifiable intangibles		$ 487,000,000
intraFUSION, BDI Pharma, LLC, and Uniprix Group [Member]
Business Acquisition [Line Items]
Net purchase consideration					480,000,000
Goodwill					235,000,000
Acquired identifiable intangibles					$ 118,000,000
Uniprix Group | CANADA
Business Acquisition [Line Items]
Number of Pharmacies Operated | pharmacy					375	375
Rexall Health | CANADA
Business Acquisition [Line Items]
Net purchase consideration			$ 2,100,000,000	CAD 2,900
Assets acquired as of the acquisition date, excluding goodwill and intangibles					$ 560,000,000
Liabilities assumed as of the acquisition date					$ 210,000,000
Goodwill			948,000,000
Acquired identifiable intangibles			$ 872,000,000
Number of retail pharmacies | pharmacy			450
Number of retail pharmacies sold | pharmacy					27	27
Gain (loss) on sale of stores					$ 0
Vantage Oncology Holdings, LLC (“Vantage”), Biologics, Inc., UDG Healthcare Plc (“UDG”) and Other Businesses
Business Acquisition [Line Items]
Net purchase consideration							$ 2,000,000,000
Additional amount, Up to | CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Contingent consideration								$ 160,000,000
Customer relationships | CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Weighted average life of intangibles		17 years
Customer relationships | Rexall Health | CANADA
Business Acquisition [Line Items]
Weighted average life of intangibles			19 years	19 years
Trade Names | Rexall Health | CANADA
Business Acquisition [Line Items]
Weighted average life of intangibles			19 years	19 years
Estimate of Fair Value | CoverMyMeds, LLC (CMM)
Business Acquisition [Line Items]
Contingent consideration		$ 113,000,000
Third Party Buyer | Rexall Health | CANADA
Business Acquisition [Line Items]
Proceeds from sale of stores					94,000,000				CAD 116
Third Party Seller of Rexall Health | Rexall Health | CANADA
Business Acquisition [Line Items]
Proceeds for settlement of post-closing purchase price adjustment					$ 119,000,000	CAD 147
Subsequent Event | RxCrossroads
Business Acquisition [Line Items]
Net purchase consideration	$ 724,000,000