Commitments and Contingent Liabilities - Narrative (Details)							2 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) case stateAttorney state	Sep. 28, 2021 USD ($) distributor	Sep. 04, 2021 state distributor territory	Jul. 21, 2021 USD ($) distributor	Jul. 20, 2021 USD ($) distributor	May 17, 2013 USD ($)	Sep. 30, 2021 USD ($) case stateAttorney state	Sep. 30, 2021 USD ($) case stateAttorney state	Sep. 30, 2021 USD ($) case stateAttorney state	Mar. 31, 2021 USD ($)	Aug. 13, 2019 fax fax_number	Apr. 30, 2018 USD ($)
National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Pre-tax expenses related to estimated litigation liability								$ 112,000,000	$ 186,000,000	$ 8,100,000,000
After-tax expenses related to estimated litigation liability								93,000,000	155,000,000	$ 6,800,000,000
Total litigation liabilities	$ 8,218,000,000						$ 8,218,000,000	8,218,000,000	8,218,000,000
State Opioid Statutes
Loss Contingencies [Line Items]
Aggregate annual surcharge on licensed manufacturers and distributors of opioids												$ 100,000,000
Total litigation liabilities	50,000,000						50,000,000	50,000,000	50,000,000
After-tax accrual	$ 37,000,000						$ 37,000,000	$ 37,000,000	$ 37,000,000
National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Complaints filed against the entity | case	2,800						2,800	2,800	2,800
Number of states in which court cases are pending | state			42
Number of other national distributors named in suit | distributor			2	2
Number of distributors | distributor				3
Award payable under proposed framework				$ 7,900,000,000
Portion of settlement to be paid by the Company (percent)				38.10%
Portion of settlement award to be used by state and local government for remediation (percent)				85.00%
Number of eligible states | state			49
Number of territories in which court cases are pending | territory			5
Number of days for decision of settlement			30 days
Settlement payment							$ 354,000,000
National Prescription Opioid Litigation | State of New York
Loss Contingencies [Line Items]
Number of other national distributors named in suit | distributor					2
Award payable under proposed framework					$ 1,200,000,000
Portion of settlement to be paid by the Company (percent)					38.10%
Settlement payment	$ 35,000,000
National Prescription Opioid Litigation | State of Ohio
Loss Contingencies [Line Items]
Number of other national distributors named in suit | distributor		2
Award payable under proposed framework		$ 881,000,000
National Prescription Opioid Litigation | Cherokee Nation
Loss Contingencies [Line Items]
Number of other national distributors named in suit | distributor		2
Award payable under proposed framework		$ 75,000,000
Portion of settlement to be paid by the Company (percent)		38.10%
Payment term		6 years 6 months
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
Canada | National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Complaints filed against the entity | case	4						4	4	4
Canada | National Prescription Opioid Litigation | Governmental entities
Loss Contingencies [Line Items]
Complaints filed against the entity | case	3						3	3	3
Canada | National Prescription Opioid Litigation | An individual
Loss Contingencies [Line Items]
Complaints filed against the entity | case	1						1	1	1
Three Largest U.S. Pharmaceutical Distributors | National Prescription Opioid Litigation
Loss Contingencies [Line Items]
Award payable under proposed framework				$ 21,000,000,000
Period over which award would be payable under proposed framework				18 years
Pending
Loss Contingencies [Line Items]
Complaints filed against the entity | case	350						350	350	350
Number of states in which court cases are pending | state	38						38	38	38
Number of attorney generals that have filed claims | stateAttorney	26						26	26	26
Pending | Canada
Loss Contingencies [Line Items]
Complaints filed against the entity | case	4						4	4	4