Commitments and Contingent Liabilities	3 Months Ended
Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	Commitments and Contingent Liabilities Litigation, Government Subpoenas and Investigations As previously disclosed, the Company is a defendant in many cases alleging claims related to the distribution of controlled substances to pharmacies, often together with other pharmaceutical wholesale distributors and pharmaceutical manufacturers and retail pharmacy chains named as defendants. The plaintiffs in these actions include state attorneys general, county and city municipalities, hospitals, Indian tribes, pension funds, and third-party payors. The Company has been served with 740 complaints filed in state and federal courts throughout the United States and in Puerto Rico. Since December 5, 2017, nearly all the cases pending in federal district courts have been transferred to a multi-district litigation proceeding in the United States District Court for the Northern District of Ohio captioned In re: National Prescription Opiate Litigation, Case No. 17-md-28-04. Fifteen of the cases pending in state court in New York have been transferred to a consolidated proceeding in Suffolk County Supreme Court captioned In re Opioid Litigation, Index No. 400000/2017. On July 17, 2018, the court denied the distributors’ motion to dismiss these matters. As previously disclosed, the four shareholder derivative complaints filed in the Delaware Court of Chancery were consolidated under the caption In re McKesson Corporation Stockholder Derivative Litigation, No. 2017-0736. On May 25, 2018, the court stayed further proceedings in the matter in favor of the previously disclosed consolidated shareholder derivative action pending the United States District Court for the Northern District of California, In re McKesson Corporation Derivative Litigation, No. 4:17-cv-1850. As previously disclosed, on May 17, 2013, the Company was served with a complaint filed in the United States District Court for the Northern District of California alleging that the company sent unsolicited marketing faxes in violation of the Telephone Consumer Protection Act of 1991, as amended by the Junk Fax Protection Action of 2005, True Health Chiropractic Inc., et al. v. McKesson Corporation, et al., CV-13-02219. On August 22, 2016, the court denied plaintiffs’ motion for class certification. On November 16, 2016, plaintiffs were granted leave to appeal that ruling to the United States Court of Appeals for the Ninth Circuit (“Ninth Circuit.”) On July 17, 2018, the Ninth Circuit affirmed in part and reversed in part the district court’s denial of class certification and remanded the case to the district court for further proceedings. On June 15, 2018, an amended complaint was filed in the United States District Court for the Southern District of Illinois alleging that McKesson Medical-Surgical Inc., among others, violated the Sherman Act by restraining trade in the sale of safety and conventional syringes and safety IV catheters. Marion Diagnostic Center, LLC v. Becton, Dickinson, and Co., No. 18:1059. The action is filed on behalf of a purported class of purchasers, and seeks treble damages and further relief, all in unspecified amounts. 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 matter. 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 healthcare industry. Examples of such subpoenas and investigations are included in the Company’s 2018 Annual Report on Form 10-K. New York Opioid Statute Legislative, regulatory or industry measures to address the misuse of prescription opioid medications could affect the Company’s business in ways that we may not be able to predict. For example, in April 2018, the State of New York adopted the Opioid Stewardship Act (the “OSA”) which required the creation of an aggregate $100 million annual surcharge on all manufacturers and distributors licensed to sell or distribute opioids in New York. The initial surcharge payment is due on January 1, 2019 for opioids sold or distributed during calendar year 2017. It is uncertain at this point in time what proportion of this estimated liability will be ultimately borne by the Company because the Company’s share of the surcharge depends heavily on what other licensees report. The Company has estimated and reflected a liability for the OSA surcharge in its accompanying condensed consolidated financial statements. However, it is possible that the ultimate costs may exceed or be less than the reserve. Moreover, on July 6, 2018, the Healthcare Distribution Alliance filed a lawsuit challenging the constitutionality of the law and seeking an injunction against its enforcement. We are not able to predict whether this lawsuit will be successful. In addition, other states are considering legislation that could require us to pay taxes or assessments on the distribution of opioid medications in those states. These proposed bills vary in the amounts and the means of calculation. Liabilities for taxes or assessments under any such laws will likely have an adverse impact on our results of operations, unless we are able to mitigate them through operational changes or commercial arrangements where permitted.

Commitments and Contingent Liabilities

Litigation, Government Subpoenas and Investigations

As previously disclosed, the Company is a defendant in many cases alleging claims related to the distribution of controlled substances to pharmacies, often together with other pharmaceutical wholesale distributors and pharmaceutical manufacturers and retail pharmacy chains named as defendants. The plaintiffs in these actions include state attorneys general, county and city municipalities, hospitals, Indian tribes, pension funds, and third-party payors. The Company has been served with 740 complaints filed in state and federal courts throughout the United States and in Puerto Rico. Since December 5, 2017, nearly all the cases pending in federal district courts have been transferred to a multi-district litigation proceeding in the United States District Court for the Northern District of Ohio captioned In re: National Prescription Opiate Litigation, Case No. 17-md-28-04. Fifteen of the cases pending in state court in New York have been transferred to a consolidated proceeding in Suffolk County Supreme Court captioned In re Opioid Litigation, Index No. 400000/2017. On July 17, 2018, the court denied the distributors’ motion to dismiss these matters.

As previously disclosed, the four shareholder derivative complaints filed in the Delaware Court of Chancery were consolidated under the caption In re McKesson Corporation Stockholder Derivative Litigation, No. 2017-0736. On May 25, 2018, the court stayed further proceedings in the matter in favor of the previously disclosed consolidated shareholder derivative action pending the United States District Court for the Northern District of California, In re McKesson Corporation Derivative Litigation, No. 4:17-cv-1850.

As previously disclosed, on May 17, 2013, the Company was served with a complaint filed in the United States District Court for the Northern District of California alleging that the company sent unsolicited marketing faxes in violation of the Telephone Consumer Protection Act of 1991, as amended by the Junk Fax Protection Action of 2005, True Health Chiropractic Inc., et al. v. McKesson Corporation, et al., CV-13-02219. On August 22, 2016, the court denied plaintiffs’ motion for class certification. On November 16, 2016, plaintiffs were granted leave to appeal that ruling to the United States Court of Appeals for the Ninth Circuit (“Ninth Circuit.”) On July 17, 2018, the Ninth Circuit affirmed in part and reversed in part the district court’s denial of class certification and remanded the case to the district court for further proceedings.

On June 15, 2018, an amended complaint was filed in the United States District Court for the Southern District of Illinois alleging that McKesson Medical-Surgical Inc., among others, violated the Sherman Act by restraining trade in the sale of safety and conventional syringes and safety IV catheters. Marion Diagnostic Center, LLC v. Becton, Dickinson, and Co., No. 18:1059. The action is filed on behalf of a purported class of purchasers, and seeks treble damages and further relief, all in unspecified amounts.

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 matter. 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 healthcare industry. Examples of such subpoenas and investigations are included in the Company’s 2018 Annual Report on Form 10-K.

New York Opioid Statute

Legislative, regulatory or industry measures to address the misuse of prescription opioid medications could affect the Company’s business in ways that we may not be able to predict. For example, in April 2018, the State of New York adopted the Opioid Stewardship Act (the “OSA”) which required the creation of an aggregate $100 million annual surcharge on all manufacturers and distributors licensed to sell or distribute opioids in New York. The initial surcharge payment is due on January 1, 2019 for opioids sold or distributed during calendar year 2017. It is uncertain at this point in time what proportion of this estimated liability will be ultimately borne by the Company because the Company’s share of the surcharge depends heavily on what other licensees report. The Company has estimated and reflected a liability for the OSA surcharge in its accompanying condensed consolidated financial statements. However, it is possible that the ultimate costs may exceed or be less than the reserve. Moreover, on July 6, 2018, the Healthcare Distribution Alliance filed a lawsuit challenging the constitutionality of the law and seeking an injunction against its enforcement. We are not able to predict whether this lawsuit will be successful. In addition, other states are considering legislation that could require us to pay taxes or assessments on the distribution of opioid medications in those states. These proposed bills vary in the amounts and the means of calculation. Liabilities for taxes or assessments under any such laws will likely have an adverse impact on our results of operations, unless we are able to mitigate them through operational changes or commercial arrangements where permitted.