Commitments and Contingent Liabilities - Narrative (Details)		1 Months Ended	3 Months Ended
	May 17, 2013 USD ($)	Oct. 31, 2020 USD ($) company	Sep. 30, 2020 USD ($) state case state_attorney county	Mar. 31, 2020 county	Jan. 14, 2020 company	Dec. 31, 2019 relator	Aug. 13, 2019 fax_number fax	Apr. 30, 2018 USD ($)
Loss Contingencies [Line Items]
Aggregate annual surcharge on licensed manufacturers and distributors of opioids								$ 100,000,000
Pre-tax accrual			$ 50,000,000
After-tax accrual			$ 37,000,000
In re: National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Complaints filed against the entity | case			2,800
Pre-tax charges			$ 82,000,000
Number of counties that filed claims | county			2
United States ex rel. Kelley, 19-cv-2233
Loss Contingencies [Line Items]
Number of relators alleging violations | relator						2
True Health Chiropractic Inc., et al. v. McKesson Corporation, et al
Loss Contingencies [Line Items]
Number of faxes remaining in the class | fax_number							9,490
Number of faxes received | fax							48,769
True Health Chiropractic Inc., et al. v. McKesson Corporation, et al | Minimum
Loss Contingencies [Line Items]
Statutory damages sought per violation	$ 500
True Health Chiropractic Inc., et al. v. McKesson Corporation, et al | Maximum
Loss Contingencies [Line Items]
Statutory damages sought per violation	$ 1,500
Pending
Loss Contingencies [Line Items]
Complaints filed against the entity | case			400
Number of states in which court cases are pending | state			36
Number of attorney generals that have filed claims | state_attorney			26
Number of county government plaintiffs | county				2
Pending | In re: National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Number of cases selected for possible remand to other federal courts | case			3
Pending | In re: National Prescription Opioid Litigation | Subsequent Event
Loss Contingencies [Line Items]
Award payable under proposed framework		$ 8,000,000,000.0
Period over which award would be payable under proposed framework		18 years
Pending | Canada
Loss Contingencies [Line Items]
Complaints filed against the entity | case			3
Pending | Three Largest U.S. Pharmaceutical Distributors | In re: National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Number of largest pharmaceutical distributors to adopt anti-diversion programs under proposed framework | company					3
Pending | Three Largest U.S. Pharmaceutical Distributors | In re: National Prescription Opioid Litigation | Subsequent Event
Loss Contingencies [Line Items]
Number of largest pharmaceutical distributors to adopt anti-diversion programs under proposed framework | company		3
Award payable under proposed framework		$ 21,000,000,000.0
Period over which award would be payable under proposed framework		18 years