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Asset Impairments and Product Alignment Charges (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Asset Impairments And Product Alignment Charges [Line Items]      
Capitalized software held for sale impairment $ 0us-gaap_CapitalizedComputerSoftwareImpairments $ 12us-gaap_CapitalizedComputerSoftwareImpairments $ 10us-gaap_CapitalizedComputerSoftwareImpairments
Technology Solutions [Member]      
Asset Impairments And Product Alignment Charges [Line Items]      
Nonrecurring charges   57us-gaap_OtherNonrecurringExpense
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
46us-gaap_OtherNonrecurringExpense
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
Product alignment charges   35mck_ProductAlignmentCharges
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Integration related costs   15us-gaap_BusinessCombinationIntegrationRelatedCosts
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Reduction in force severance charges   7us-gaap_SeveranceCosts1
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Asset impairment charges   15us-gaap_OtherAssetImpairmentCharges
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Technology Solutions [Member] | Cost of Sales [Member]      
Asset Impairments And Product Alignment Charges [Line Items]      
Nonrecurring charges   34us-gaap_OtherNonrecurringExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Capitalized software held for sale impairment     10us-gaap_CapitalizedComputerSoftwareImpairments
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
Technology Solutions [Member] | Operating Expense [Member]      
Asset Impairments And Product Alignment Charges [Line Items]      
Nonrecurring charges   23us-gaap_OtherNonrecurringExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OperatingExpenseMember
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
 
Goodwill impairment     36us-gaap_GoodwillImpairmentLoss
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OperatingExpenseMember
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember
Technology Solutions [Member] | Severance Charges Due to Reorganization [Member]      
Asset Impairments And Product Alignment Charges [Line Items]      
Reduction in force severance charges   $ 35us-gaap_SeveranceCosts1
/ mck_ProductAlignmentByTypeAxis
= mck_SeveranceChargesDuetoReorganizationMember
/ us-gaap_StatementBusinessSegmentsAxis
= mck_TechnologySolutionsMember