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Commitments and Contingent Liabilities - Narrative (Details) |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |
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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 |  |  |  |  |  |  |  |  |

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