Other Commitments and Contingent Liabilities	12 Months Ended
Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Other Commitments and Contingent Liabilities	Other Commitments and Contingent Liabilities In addition to commitments and obligations in the ordinary course of business, we are subject to various claims, other pending and potential legal actions for damages, investigations relating to governmental laws and regulations and other matters arising out of the normal conduct of our business. As described below, many of these proceedings are at preliminary stages and many seek an indeterminate amount of damages. When a loss is considered probable and reasonably estimable, we record a liability in the amount of our best estimate for the ultimate loss. However, the likelihood of a loss with respect to a particular contingency is often difficult to predict and determining a meaningful estimate of the loss or a range of loss may not be practicable based on the information available and the potential effect of future events and decisions by third parties that will determine the ultimate resolution of the contingency. Moreover, it is not uncommon for such matters to be resolved over many years, during which time relevant developments and new information must be reevaluated at least quarterly to determine both the likelihood of potential loss and whether it is possible to reasonably estimate a range of possible loss. When a loss is probable but a reasonable estimate cannot be made, disclosure of the proceeding is provided. Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. We review all contingencies at least quarterly to determine whether the likelihood of loss has changed and to assess whether a reasonable estimate of the loss or range of loss can be made. As discussed above, development of a meaningful estimate of loss or a range of potential loss is complex when the outcome is directly dependent on negotiations with or decisions by third parties, such as regulatory agencies, the court system and other interested parties. Such factors bear directly on whether it is possible to reasonably estimate a range of potential loss and boundaries of high and low estimates. We are party to the legal proceedings described below. Unless otherwise stated, we are currently unable to estimate a range of reasonably possible losses for the unresolved proceedings described below. Should any one or a combination of more than one of these proceedings be successful, or should we determine to settle any or a combination of these matters, we may be required to pay substantial sums, become subject to the entry of an injunction or be forced to change the manner in which we operate our business, which could have a material adverse impact on our financial position or results of operations. I. Litigation and Claims On August 29, 2007, PSKW, LLC filed a lawsuit against McKesson Specialty Arizona Inc. in the New York Supreme Court, New York County, alleging that McKesson Specialty Arizona misappropriated trade secrets and confidential information in launching its LoyaltyScript® program, PSKW, LLC V. McKesson Specialty Arizona Inc., Index No. 602921/07. Plaintiff later amended its complaint twice to add additional, but related claims. On August 31, 2011, McKesson Specialty Arizona moved for summary judgment on all claims. On December 23, 2013, the court dismissed PSKW’s cause of action for misappropriation of ideas. PSKW appealed this decision and on October 21, 2014, the Appellate Division reversed. On January 30, 2015, the trial court granted McKesson Specialty Arizona’s motion to strike the jury and later set trial for June 15, 2015. On April 16, 2013, the Company’s wholly-owned subsidiary, U.S. Oncology, Inc. (“USON”), was served with a third amended qui tam complaint filed in the United States District Court for the Eastern District of New York by two relators, purportedly on behalf of the United States, twenty-one states and the District of Columbia, against USON and five other defendants, alleging that USON solicited and received illegal “kickbacks” from Amgen in violation of the Anti-Kickback Statute, the False Claims Act, and various state false claims statutes, and seeking damages, treble damages, civil penalties, attorneys’ fees and costs of suit, all in unspecified amounts, United States ex rel. Piacentile v. Amgen Inc., et al., CV 04-3983 (SJ). Previously, the United States declined to intervene in the case as to all allegations and defendants except for Amgen. On February 5, 2013, the United States filed a motion to dismiss the claims pled against Amgen. On September 30, 2013, the court granted the United States’ motion to dismiss. On April 4, 2014, USON filed a motion to dismiss the claims pled against it. The court has not yet ruled on USON’s motion. On June 17, 2014, U.S. Oncology Specialty, LP (“USOS”) was served with a fifth amended qui tam complaint filed in July 2008 in the United States District Court for the Eastern District of New York by a relator against USOS, among others, alleging that USOS solicited and received illegal “kickbacks” from Amgen in violation of the Anti-Kickbacks Statute, the False Claims Act, and various state false claims statutes, and seeking damages, treble damages, civil penalties, attorneys’ fees and costs of suit, all in unspecified amounts, United States ex rel. Hanks v. Amgen, Inc., et al., CV-08-03096 (SJ). Previously, the United States declined to intervene in the case as to all allegations and defendants except for Amgen. On August 1, 2014, USOS filed a motion to dismiss the claims pled against it and the hearing occurred on October 7, 2014. The court has not yet ruled on USOS’s motion. On May 21, 2014, four hedge funds managed by Magnetar Capital filed a complaint against McKesson Deutschland GmbH & Co. KGaA (formerly known as “Dragonfly GmbH & Co. KGaA”) (“Dragonfly”), a wholly‑owned subsidiary of the Company, in a German court in Frankfurt, Germany, alleging that Dragonfly violated German takeover law in connection with the Company’s acquisition of Celesio by paying more to some holders of Celesio’s convertible bonds than it paid to the shareholders of Celesio’s stock, Magnetar Capital Master Fund Ltd. et al. v. Dragonfly GmbH & Co KGaA, No. 3-05 O 44/14. On December 5, 2014, the court fully dismissed Magnetar’s lawsuit in Dragonfly’s favor and ruled that the plaintiffs must bear the court costs and Dragonfly’s taxable lawyers’ fees. Magnetar filed a notice of appeal on January 5, 2015. II. Government Subpoenas and Investigations From time-to-time, the Company receives subpoenas or requests for information from various government agencies. The Company generally responds to such subpoenas and requests in a cooperative, thorough and timely manner. These responses sometimes require time and effort and can result in considerable costs being incurred by the Company. Such subpoenas and requests also can lead to the assertion of claims or the commencement of civil or criminal legal proceedings against the Company and other members of the health care industry, as well as to settlements. An example is the subpoena from the office of the Attorney General of West Virginia in the fourth quarter of 2015 seeking information about the Company’s distribution of controlled substances in West Virginia. The Company has provided the requested documents. In addition, in the fourth quarter of 2015, the Company reached an agreement in principle with the Drug Enforcement Administration (“DEA”), Department of Justice (“DOJ”) and various U.S. Attorney’s offices to settle all potential administrative and civil claims relating to investigations about the Company’s suspicious order reporting practices for controlled substances. The global settlement with the DEA and DOJ is subject to the execution of final settlement agreements. Under the terms of the agreement in principle, the Company has agreed to pay the sum of $150 million, implement certain remedial measures and have the following distribution centers’ DEA registrations suspended for the specified products and time periods: Aurora, Colorado: all controlled substances for three years; Livonia, Michigan: all controlled substances for two years; Washington Courthouse, Ohio: all controlled substances for the two-year period following completion of the Livonia suspension; and Lakeland, Florida: hydromorphone products for one year. Throughout the terms of these suspensions, the Company will be permitted to continue to ship controlled substances from its Livonia, Washington Courthouse and Lakeland distribution centers to customers that purchase products under its pharmaceutical prime vendor contract with the Department of Veterans Affairs. The Company expects that the suspensions will not result in a supply disruption to any customer. Customers located in the distribution center service areas described above will receive controlled substances from a different distribution center during the applicable suspension periods. As a result of our agreement in principle, during the fourth quarter of 2015, we recorded a $150 million pre-tax and after-tax charge relating to these claims. III. Environmental Matters Primarily as a result of the operation of the Company’s former chemical businesses, which were fully divested by 1987, the Company is involved in various matters pursuant to environmental laws and regulations. The Company has received claims and demands from governmental agencies relating to investigative and remedial actions purportedly required to address environmental conditions alleged to exist at six sites where it, or entities acquired by it, formerly conducted operations and the Company, by administrative order or otherwise, has agreed to take certain actions at those sites, including soil and groundwater remediation. In addition, the Company is one of multiple recipients of a New Jersey Department of Environmental Protection Agency directive and a separate United States Environmental Protection Agency directive relating to potential natural resources damages (“NRD”) associated with one of these six sites. Although the Company’s potential allocation under either directive cannot be determined at this time, it has agreed to participate with a potentially responsible party (“PRP”) group in the funding of certain tasks to support an NRD assessment, the costs of which are reflected in the aggregate estimates set forth below. Based on a determination by the Company’s environmental staff, in consultation with outside environmental specialists and counsel, the current estimate of the Company’s probable loss associated with the remediation costs for these six sites is $7 million, net of amounts anticipated from third parties. The $7 million is expected to be paid out between April 2015 and March 2035. The Company’s estimated probable loss for these environmental matters has been entirely accrued for in the accompanying consolidated balance sheets. In addition, the Company has been designated as a PRP under the Superfund law for environmental assessment and cleanup costs as the result of its alleged disposal of hazardous substances at 14 sites. With respect to these sites, numerous other PRPs have similarly been designated and while the current state of the law potentially imposes joint and several liability upon PRPs, as a practical matter, costs of these sites are typically shared with other PRPs. At one of these sites, the United States Environmental Protection Agency has selected a preferred remedy with an estimated cost of approximately $70 million. It is not certain at this point in time what proportion of this estimated liability will be borne by the Company or by the other PRPs. Accordingly, the Company’s estimated probable loss at those 14 sites is approximately $22 million, which has been entirely accrued for in the accompanying consolidated balance sheets. However, it is possible that the ultimate costs of these matters may exceed or be less than the reserves. IV. Value Added Tax Assessments We operate in various countries outside the United States which collect value added taxes (“VAT”). The determination of the manner in which a VAT applies to our foreign operations is subject to varying interpretations arising from the complex nature of the tax laws. We have received assessments for VAT which are in various stages of appeal. We disagree with these assessments and believe that we have strong legal arguments to defend our tax positions. Certain VAT assessments relate to years covered by an indemnification agreement. Due to the complex nature of the tax laws, it is not possible to estimate the outcome of these matters. However, based on the currently available information, we believe the ultimate outcome of these matters will not have a material adverse effect on our financial position, cash flows or results of operations. V. Average Wholesale Price (“AWP”) Litigation The Company has a reserve relating to AWP public entity claims, which is reviewed at least quarterly and whenever events or circumstances indicate changes. We recorded nil, $68 million and $72 million of pre-tax charges relating to changes in the Company’s AWP litigation reserve, including accrued interest, in 2015, 2014 and 2013. All charges were recorded in operating expenses within our Distribution Solutions segment. Cash payments of nil, $105 million and $483 million were made in 2015, 2014 and 2013. At March 31, 2015, the reserve for this matter was not material; at March 31, 2014, the reserve was $42 million. VI. Other Matters The Company is involved in various other litigation and governmental proceedings, not described above, that arise in the normal course of business. While it is not possible to determine the ultimate outcome or the duration of any such litigation or governmental proceedings, the Company believes, based on current knowledge and the advice of counsel, that such litigation and proceedings will not have a material impact on the Company’s financial position or results of operations.

Other Commitments and Contingent Liabilities

In addition to commitments and obligations in the ordinary course of business, we are subject to various claims, other pending and potential legal actions for damages, investigations relating to governmental laws and regulations and other matters arising out of the normal conduct of our business. As described below, many of these proceedings are at preliminary stages and many seek an indeterminate amount of damages.

When a loss is considered probable and reasonably estimable, we record a liability in the amount of our best estimate for the ultimate loss. However, the likelihood of a loss with respect to a particular contingency is often difficult to predict and determining a meaningful estimate of the loss or a range of loss may not be practicable based on the information available and the potential effect of future events and decisions by third parties that will determine the ultimate resolution of the contingency. Moreover, it is not uncommon for such matters to be resolved over many years, during which time relevant developments and new information must be reevaluated at least quarterly to determine both the likelihood of potential loss and whether it is possible to reasonably estimate a range of possible loss. When a loss is probable but a reasonable estimate cannot be made, disclosure of the proceeding is provided.

Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. We review all contingencies at least quarterly to determine whether the likelihood of loss has changed and to assess whether a reasonable estimate of the loss or range of loss can be made. As discussed above, development of a meaningful estimate of loss or a range of potential loss is complex when the outcome is directly dependent on negotiations with or decisions by third parties, such as regulatory agencies, the court system and other interested parties. Such factors bear directly on whether it is possible to reasonably estimate a range of potential loss and boundaries of high and low estimates.

We are party to the legal proceedings described below. Unless otherwise stated, we are currently unable to estimate a range of reasonably possible losses for the unresolved proceedings described below. Should any one or a combination of more than one of these proceedings be successful, or should we determine to settle any or a combination of these matters, we may be required to pay substantial sums, become subject to the entry of an injunction or be forced to change the manner in which we operate our business, which could have a material adverse impact on our financial position or results of operations.

I. Litigation and Claims

On August 29, 2007, PSKW, LLC filed a lawsuit against McKesson Specialty Arizona Inc. in the New York Supreme Court, New York County, alleging that McKesson Specialty Arizona misappropriated trade secrets and confidential information in launching its LoyaltyScript® program, PSKW, LLC V. McKesson Specialty Arizona Inc., Index No. 602921/07. Plaintiff later amended its complaint twice to add additional, but related claims. On August 31, 2011, McKesson Specialty Arizona moved for summary judgment on all claims. On December 23, 2013, the court dismissed PSKW’s cause of action for misappropriation of ideas. PSKW appealed this decision and on October 21, 2014, the Appellate Division reversed. On January 30, 2015, the trial court granted McKesson Specialty Arizona’s motion to strike the jury and later set trial for June 15, 2015.

On April 16, 2013, the Company’s wholly-owned subsidiary, U.S. Oncology, Inc. (“USON”), was served with a third amended qui tam complaint filed in the United States District Court for the Eastern District of New York by two relators, purportedly on behalf of the United States, twenty-one states and the District of Columbia, against USON and five other defendants, alleging that USON solicited and received illegal “kickbacks” from Amgen in violation of the Anti-Kickback Statute, the False Claims Act, and various state false claims statutes, and seeking damages, treble damages, civil penalties, attorneys’ fees and costs of suit, all in unspecified amounts, United States ex rel. Piacentile v. Amgen Inc., et al., CV 04-3983 (SJ). Previously, the United States declined to intervene in the case as to all allegations and defendants except for Amgen. On February 5, 2013, the United States filed a motion to dismiss the claims pled against Amgen. On September 30, 2013, the court granted the United States’ motion to dismiss. On April 4, 2014, USON filed a motion to dismiss the claims pled against it. The court has not yet ruled on USON’s motion.

On June 17, 2014, U.S. Oncology Specialty, LP (“USOS”) was served with a fifth amended qui tam complaint filed in July 2008 in the United States District Court for the Eastern District of New York by a relator against USOS, among others, alleging that USOS solicited and received illegal “kickbacks” from Amgen in violation of the Anti-Kickbacks Statute, the False Claims Act, and various state false claims statutes, and seeking damages, treble damages, civil penalties, attorneys’ fees and costs of suit, all in unspecified amounts, United States ex rel. Hanks v. Amgen, Inc., et al., CV-08-03096 (SJ). Previously, the United States declined to intervene in the case as to all allegations and defendants except for Amgen. On August 1, 2014, USOS filed a motion to dismiss the claims pled against it and the hearing occurred on October 7, 2014. The court has not yet ruled on USOS’s motion.

On May 21, 2014, four hedge funds managed by Magnetar Capital filed a complaint against McKesson Deutschland GmbH & Co. KGaA (formerly known as “Dragonfly GmbH & Co. KGaA”) (“Dragonfly”), a wholly‑owned subsidiary of the Company, in a German court in Frankfurt, Germany, alleging that Dragonfly violated German takeover law in connection with the Company’s acquisition of Celesio by paying more to some holders of Celesio’s convertible bonds than it paid to the shareholders of Celesio’s stock, Magnetar Capital Master Fund Ltd. et al. v. Dragonfly GmbH & Co KGaA, No. 3-05 O 44/14. On December 5, 2014, the court fully dismissed Magnetar’s lawsuit in Dragonfly’s favor and ruled that the plaintiffs must bear the court costs and Dragonfly’s taxable lawyers’ fees. Magnetar filed a notice of appeal on January 5, 2015.

II. Government Subpoenas and Investigations

From time-to-time, the Company receives subpoenas or requests for information from various government agencies. The Company generally responds to such subpoenas and requests in a cooperative, thorough and timely manner. These responses sometimes require time and effort and can result in considerable costs being incurred by the Company. Such subpoenas and requests also can lead to the assertion of claims or the commencement of civil or criminal legal proceedings against the Company and other members of the health care industry, as well as to settlements. An example is the subpoena from the office of the Attorney General of West Virginia in the fourth quarter of 2015 seeking information about the Company’s distribution of controlled substances in West Virginia. The Company has provided the requested documents.

In addition, in the fourth quarter of 2015, the Company reached an agreement in principle with the Drug Enforcement Administration (“DEA”), Department of Justice (“DOJ”) and various U.S. Attorney’s offices to settle all potential administrative and civil claims relating to investigations about the Company’s suspicious order reporting practices for controlled substances. The global settlement with the DEA and DOJ is subject to the execution of final settlement agreements. Under the terms of the agreement in principle, the Company has agreed to pay the sum of $150 million, implement certain remedial measures and have the following distribution centers’ DEA registrations suspended for the specified products and time periods: Aurora, Colorado: all controlled substances for three years; Livonia, Michigan: all controlled substances for two years; Washington Courthouse, Ohio: all controlled substances for the two-year period following completion of the Livonia suspension; and Lakeland, Florida: hydromorphone products for one year. Throughout the terms of these suspensions, the Company will be permitted to continue to ship controlled substances from its Livonia, Washington Courthouse and Lakeland distribution centers to customers that purchase products under its pharmaceutical prime vendor contract with the Department of Veterans Affairs. The Company expects that the suspensions will not result in a supply disruption to any customer. Customers located in the distribution center service areas described above will receive controlled substances from a different distribution center during the applicable suspension periods. As a result of our agreement in principle, during the fourth quarter of 2015, we recorded a $150 million pre-tax and after-tax charge relating to these claims.

III. Environmental Matters

Primarily as a result of the operation of the Company’s former chemical businesses, which were fully divested by 1987, the Company is involved in various matters pursuant to environmental laws and regulations. The Company has received claims and demands from governmental agencies relating to investigative and remedial actions purportedly required to address environmental conditions alleged to exist at six sites where it, or entities acquired by it, formerly conducted operations and the Company, by administrative order or otherwise, has agreed to take certain actions at those sites, including soil and groundwater remediation. In addition, the Company is one of multiple recipients of a New Jersey Department of Environmental Protection Agency directive and a separate United States Environmental Protection Agency directive relating to potential natural resources damages (“NRD”) associated with one of these six sites. Although the Company’s potential allocation under either directive cannot be determined at this time, it has agreed to participate with a potentially responsible party (“PRP”) group in the funding of certain tasks to support an NRD assessment, the costs of which are reflected in the aggregate estimates set forth below.

Based on a determination by the Company’s environmental staff, in consultation with outside environmental specialists and counsel, the current estimate of the Company’s probable loss associated with the remediation costs for these six sites is $7 million, net of amounts anticipated from third parties. The $7 million is expected to be paid out between April 2015 and March 2035. The Company’s estimated probable loss for these environmental matters has been entirely accrued for in the accompanying consolidated balance sheets.

In addition, the Company has been designated as a PRP under the Superfund law for environmental assessment and cleanup costs as the result of its alleged disposal of hazardous substances at 14 sites. With respect to these sites, numerous other PRPs have similarly been designated and while the current state of the law potentially imposes joint and several liability upon PRPs, as a practical matter, costs of these sites are typically shared with other PRPs. At one of these sites, the United States Environmental Protection Agency has selected a preferred remedy with an estimated cost of approximately $70 million. It is not certain at this point in time what proportion of this estimated liability will be borne by the Company or by the other PRPs. Accordingly, the Company’s estimated probable loss at those 14 sites is approximately $22 million, which has been entirely accrued for in the accompanying consolidated balance sheets. However, it is possible that the ultimate costs of these matters may exceed or be less than the reserves.

IV. Value Added Tax Assessments

We operate in various countries outside the United States which collect value added taxes (“VAT”). The determination of the manner in which a VAT applies to our foreign operations is subject to varying interpretations arising from the complex nature of the tax laws. We have received assessments for VAT which are in various stages of appeal. We disagree with these assessments and believe that we have strong legal arguments to defend our tax positions. Certain VAT assessments relate to years covered by an indemnification agreement. Due to the complex nature of the tax laws, it is not possible to estimate the outcome of these matters. However, based on the currently available information, we believe the ultimate outcome of these matters will not have a material adverse effect on our financial position, cash flows or results of operations.

V. Average Wholesale Price (“AWP”) Litigation

The Company has a reserve relating to AWP public entity claims, which is reviewed at least quarterly and whenever events or circumstances indicate changes. We recorded nil, $68 million and $72 million of pre-tax charges relating to changes in the Company’s AWP litigation reserve, including accrued interest, in 2015, 2014 and 2013. All charges were recorded in operating expenses within our Distribution Solutions segment. Cash payments of nil, $105 million and $483 million were made in 2015, 2014 and 2013. At March 31, 2015, the reserve for this matter was not material; at March 31, 2014, the reserve was $42 million.

VI. Other Matters

The Company is involved in various other litigation and governmental proceedings, not described above, that arise in the normal course of business. While it is not possible to determine the ultimate outcome or the duration of any such litigation or governmental proceedings, the Company believes, based on current knowledge and the advice of counsel, that such litigation and proceedings will not have a material impact on the Company’s financial position or results of operations.