Goodwill And Intangible Assets, Net (Information Regarding Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Dec. 31, 2014	Mar. 31, 2014
Intangible assets
Gross Carrying Amount	$ 5,549	$ 6,353
Accumulated Amortization	(1,685)	(1,331)
Net Carrying Amount	3,864us-gaap_FiniteLivedIntangibleAssetsNet	5,022us-gaap_FiniteLivedIntangibleAssetsNet
Customer lists
Intangible assets
Weighted Average Remaining Amortization Period (years)	9 years
Gross Carrying Amount	2,880	3,384
Accumulated Amortization	(1,070)	(863)
Net Carrying Amount	1,810	2,521
Service agreements
Intangible assets
Weighted Average Remaining Amortization Period (years)	16 years
Gross Carrying Amount	980	995
Accumulated Amortization	(207)	(173)
Net Carrying Amount	773	822
Pharmacy Licenses
Intangible assets
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	958	1,219
Accumulated Amortization	(58)	(11)
Net Carrying Amount	900	1,208
Trademarks and trade names
Intangible assets
Weighted Average Remaining Amortization Period (years)	15 years
Gross Carrying Amount	349	371
Accumulated Amortization	(79)	(59)
Net Carrying Amount	270	312
Technology-Based Intangible Assets
Intangible assets
Weighted Average Remaining Amortization Period (years)	3 years
Gross Carrying Amount	213	219
Accumulated Amortization	(182)	(173)
Net Carrying Amount	31	46
Other
Intangible assets
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	169	165
Accumulated Amortization	(89)	(52)
Net Carrying Amount	$ 80	$ 113

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNetAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Remaining amortization period of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=mck_PharmacyLicensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerListsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OtherIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_ServiceAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TechnologyBasedIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksAndTradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: