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Significant Accounting Policies (Narrative) (Details) (USD $) | 12 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Significant Accounting Policies [Line Items] |  |  |
LIFO inventory, percentage | 73.00%us-gaap_PercentageOfLIFOInventory | 67.00%us-gaap_PercentageOfLIFOInventory |
LIFO reserve | $ 768,000,000us-gaap_InventoryLIFOReserve | $ 431,000,000us-gaap_InventoryLIFOReserve |
LIFO expense | 337,000,000us-gaap_InventoryLIFOReservePeriodCharge | 311,000,000us-gaap_InventoryLIFOReservePeriodCharge | 13,000,000us-gaap_InventoryLIFOReservePeriodCharge
LIFO inventory, excess of market |  |  | 60,000,000us-gaap_ExcessOfReplacementOrCurrentCostsOverStatedLIFOValue
LIFO to market adjustment |  | 60,000,000mck_InventoryLIFOtoMarketAdjustment |
Capitalized software held for sale, useful life | 3 years |  |
Capitalized software held for internal use, net | 435,000,000us-gaap_CapitalizedComputerSoftwareNet | 508,000,000us-gaap_CapitalizedComputerSoftwareNet |
Capitalized software held for internal use, accumulated amortization | 1,112,000,000us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization | 1,004,000,000us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization |
Sales returns from customers | 2,700,000,000us-gaap_SalesReturnsGoods | 1,900,000,000us-gaap_SalesReturnsGoods | 1,900,000,000us-gaap_SalesReturnsGoods
Supplier reserves | $ 167,000,000mck_SupplierReserves | $ 181,000,000mck_SupplierReserves |
Tax benefits recognized from uncertain tax positions, threshold | 50.00%mck_TaxRecognizedPercentLikelyBeingRealized |  |
Business combinations, percent consolidated | 100.00%mck_BusinessCombinationConsolidationPercent |  |
Minimum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Property, plant and equipment, useful life | 1 year |  |
Intangible assets, useful life | 1 year |  |
Capitalized software held for internal use, useful life | 1 year |  |
Maximum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Property, plant and equipment, useful life | 30 years |  |
Intangible assets, useful life | 38 years |  |
Capitalized software held for internal use, useful life | 10 years |  |
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Concentration risk, percentage | 44.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |
Accounts Receivable [Member] | Customer Concentration Risk [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Concentration risk, percentage | 36.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |
Largest Customer [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Concentration risk, percentage | 15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = mck_LargestCustomerMember |  |
Concentration risk, customer name | CVS Caremark Corporation (“CVS”) |  |
Largest Customer [Member] | Accounts Receivable [Member] | Customer Concentration Risk [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Concentration risk, percentage | 14.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = mck_LargestCustomerMember |  |
Concentration risk, customer name | CVS |  |

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- Definition Capitalized Software Held for Internal Use, Useful Life + References No definition available. + Details
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- Definition Capitalized Software Held for Sale, Useful Life + References No definition available. + Details
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- Definition For each balance sheet presented, the amount of accumulated amortization for capitalized computer software costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 985 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Description of risks that arise due to the volume of business transacted with a particular customer. At a minimum, the description informs financial statement users of the general nature of the risk, but excludes "Information about Major Customers" that may be disclosed elsewhere (for instance, segment disclosures). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6327-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 + Details
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- Definition The excess of replacement or current cost over the stated LIFO (last in first out) inventory value when the LIFO inventory method is utilized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(c)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph c -Article 5 + Details
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- Definition The change in the inventory reserve representing the cumulative difference in cost between the first in, first out and the last in, first out inventory valuation methods, which change has been reflected in the statement of income during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6b) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6a) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6c) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section L + Details
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- Definition The percentage of LIFO (last in first out) inventory to total inventory as of the balance sheet date if other than 100 percent. + References No definition available. + Details
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- Definition The aggregate refunds recognized during an accounting period due to goods returned by customers (other than under warranty provisions). Returns are a deduction from gross revenue in arriving at net revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(a)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 + Details
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