Document and Entity Information	9 Months Ended
	Dec. 31, 2018 shares
Document And Entity Information [Abstract]
Entity Registrant Name	MCKESSON CORP
Entity Central Index Key	0000927653
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding (Cover)	191,825,272