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Other Commitments and Contingent Liabilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 3 Months Ended
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2015
Loss Contingencies [Line Items] |  |  |  |
Claims and litigation charges | $ 150us-gaap_LossContingencyLossInPeriod | $ 68us-gaap_LossContingencyLossInPeriod | $ 72us-gaap_LossContingencyLossInPeriod |
Anti-Kickback Claim [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Loss Contingency Number of States Filed On Behalf Of | 21mck_LossContingencyNumberofStatesFiledOnBehalfOf / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AntiKickbackClaimMember |  |  |
Loss Contingency Number of Relators | 2mck_LossContingencyNumberofRelators / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AntiKickbackClaimMember |  |  |
Loss Contingency Number of Additional Defendants | 5mck_LossContingencyNumberofAdditionalDefendants / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AntiKickbackClaimMember |  |  |
Controlled Substance Investigation [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Claims and litigation charges | 150us-gaap_LossContingencyLossInPeriod / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_ControlledSubstanceInvestigationMember |  |  | 150us-gaap_LossContingencyLossInPeriod / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_ControlledSubstanceInvestigationMember
Claims and litigation charges, net of tax | 150mck_LossContingencyLossinPeriodNetofTax / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_ControlledSubstanceInvestigationMember |  |  |
Environmental Litigation [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Chemical conditions sites, number | 6mck_SiteContingencyNumberOfSites / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember |  |  |
Remediation costs | 7us-gaap_AccrualForEnvironmentalLossContingenciesGross / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember |  |  | 7us-gaap_AccrualForEnvironmentalLossContingenciesGross / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember
Hazardous substance sites, number | 14mck_HazardousSubstanceSites / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember |  |  |
Estimated environmental assessment and cleanup costs | 70mck_EstimatedEnvironmentalAssessmentAndCleanupCosts / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember |  |  |
Estimated loss | 22us-gaap_AccrualForEnvironmentalLossContingenciesComponentAmount / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember |  |  | 22us-gaap_AccrualForEnvironmentalLossContingenciesComponentAmount / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_EnvironmentalLitigationMember
Environmental Litigation [Member] | Minimum [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Site Contingency, Time Frame of Disbursements | 2015-04-01 |  |  |
Environmental Litigation [Member] | Maximum [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Site Contingency, Time Frame of Disbursements | 2035-03-31 |  |  |
Average Wholesale Price Litigation [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Claims and litigation charges | $ 0us-gaap_LossContingencyLossInPeriod / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AverageWholesalePriceLitigationMember | $ 68us-gaap_LossContingencyLossInPeriod / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AverageWholesalePriceLitigationMember | $ 72us-gaap_LossContingencyLossInPeriod / us-gaap_LossContingenciesByNatureOfContingencyAxis = mck_AverageWholesalePriceLitigationMember |

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