Commitments and Contingent Liabilities - Narrative (Details)		1 Months Ended	3 Months Ended	9 Months Ended
	May 17, 2013 USD ($)	Oct. 31, 2020 USD ($) company	Dec. 31, 2020 USD ($) stateAttorney case state	Dec. 31, 2020 USD ($) stateAttorney case state	Mar. 31, 2020 county	Jan. 14, 2020 company	Dec. 31, 2019 county	Aug. 13, 2019 fax_number fax	Apr. 30, 2018 USD ($)	Dec. 30, 2017 investmentFund	Dec. 29, 2017 investmentFund
Loss Contingencies [Line Items]
Number of counties that filed claims | county							2
Aggregate annual surcharge on licensed manufacturers and distributors of opioids									$ 100,000,000
Pre-tax accrual			$ 50,000,000	$ 50,000,000
After-tax accrual			37,000,000	37,000,000
National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Pre-tax expenses related to estimated litigation liability			8,100,000,000	8,100,000,000
After-tax expenses related to estimated litigation liability			$ 6,700,000,000	$ 6,700,000,000
National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Complaints filed against the entity | case			2,900	2,900
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
Polygon European Equity Opportunity Master Fund et al. v. McKesson Europe Holdings GmbH & Co. KGaA
Loss Contingencies [Line Items]
Number of investment funds that filed claims | investmentFund										4	2
Canada
Loss Contingencies [Line Items]
Complaints filed against the entity | case			3	3
Pending
Loss Contingencies [Line Items]
Complaints filed against the entity | case			400	400
Number of states in which court cases are pending | state			38	38
Number of attorney generals that have filed claims | stateAttorney			26	26
Number of county government plaintiffs | county					2
Pending | National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Number of cases selected for possible remand to other federal courts | case			3	3
Award payable under proposed framework		$ 8,000,000,000.0
Settlement award anticipated to be used to remediate the opioid crisis (percent)		90.00%
Pending | Canada
Loss Contingencies [Line Items]
Complaints filed against the entity | case			3	3
Pending | Three Largest U.S. Pharmaceutical Distributors | National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Number of largest pharmaceutical distributors to adopt anti-diversion programs under proposed framework | company		3				3
Award payable under proposed framework		$ 21,000,000,000.0
Period over which award would be payable under proposed framework		18 years