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Noncontrolling Interests Noncontrolling Interests (Changes in Noncontrolling Interests) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Jun. 30, 2014
Mar. 31, 2015
Noncontrolling Interest [Line Items]      
Balance, March 31, 2014   $ 1,796us-gaap_MinorityInterest $ 1,796us-gaap_MinorityInterest
NCI change from shares acquired     (62)us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent
Reclassification from total equity to redeemable noncontrolling interests     (1,500)mck_ReclassificationfromPermanentEquity
Noncontrolling interests, ending balance 84us-gaap_MinorityInterest   84us-gaap_MinorityInterest
Celesio [Member]      
Noncontrolling Interest [Line Items]      
Other comprehensive income, NCI portion     (138)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest
/ dei_LegalEntityAxis
= mck_CelesioMember
NCI change from shares acquired $ (9)us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent
/ dei_LegalEntityAxis
= mck_CelesioMember		 $ (35)us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent
/ dei_LegalEntityAxis
= mck_CelesioMember