Goodwill Impairment Charges	9 Months Ended
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill Impairment Charges	Goodwill Impairment Charges Goodwill impairment testing is conducted at the reporting unit level, which is generally defined as an operating segment or at one level below an operating segment (also known as a component), for which discrete financial information is available and segment management regularly reviews the operating results of that reporting unit. We evaluate goodwill for impairment on an annual basis as of January 1 each year and at an interim date, if indicators of impairment exist. McKesson Europe AG (“McKesson Europe”) During the second quarter of 2018, our McKesson Europe reporting unit within our Distribution Solutions segment experienced a decline in its estimated future cash flows, primarily in our United Kingdom (“U.K.”) retail business, driven by significant government reimbursement reductions affecting retail pharmacy economics across the U.K. market. Accordingly, we performed an interim one-step goodwill impairment test in accordance with the amended goodwill guidance for this reporting unit prior to our annual impairment test. As a result of the test, the estimated fair value of this reporting unit was determined to be lower than the carrying value. In the second quarter of 2018, we recorded a non-cash pre-tax and after-tax charge of $350 million to impair the carrying value of this reporting unit’s goodwill under the caption, “Goodwill Impairment Charges” in the accompanying condensed consolidated statement of operations. There were no tax benefits associated with the goodwill impairment charge. The fair value of the reporting unit was determined using a combination of an income approach based on a discounted cash flow (“DCF”) model and a market approach based on guideline public companies’ revenues and earnings before interest, tax, depreciation and amortization multiples. Fair value estimates result from a complex series of judgments about future events and uncertainties and rely heavily on estimates and assumptions that have been deemed reasonable by management as of the measurement date. Any changes in key assumptions, including failure to improve operations of certain retail pharmacy stores, additional government reimbursement reductions, deterioration in the financial market, an increase in interest rates or an increase in the cost of equity financing by market participants within the industry, or other unanticipated events and circumstances, may affect such estimates. Fair value assessments of the reporting unit are considered a Level 3 measurement due to the significance of unobservable inputs developed using company specific information. The discount rate and terminal growth rate used in our 2018 second quarter impairment testing for this reporting unit were 7.5% and 1.25% compared to 7.0% and 1.5% in our 2017 annual impairment test. No additional significant indicators of goodwill impairment exist during the third quarter of 2018. At December 31, 2017, the McKesson Europe reporting unit had a remaining goodwill balance of $2,692 million. Other risks, expenses and future developments that we were unable to anticipate as of the interim testing date in the second quarter of 2018 may require us to further revise the future projected cash flows, which could adversely affect the fair value of this reporting unit in future periods. As a result, we may be required to record additional impairment charges. Refer to Financial Note 4, “Restructuring and Asset Impairment Charges,” for more information. Enterprise Information Solutions In conjunction with the Healthcare Technology Net Asset Exchange, we evaluated strategic options for our EIS business, which was a reporting unit within our Technology Solutions segment during 2017. In the second quarter of 2017, we recorded a non-cash pre-tax charge of $290 million ($282 million after-tax) to impair the carrying value of this reporting unit’s goodwill. The impairment primarily resulted from a decline in estimated cash flows. The amount of goodwill impairment for the EIS business was determined under the former accounting guidance on goodwill impairment testing, and computed as the excess of the carrying value of the reporting unit’s goodwill over the implied fair value of its goodwill. The charge was recorded under the caption, “Goodwill Impairment Charges,” within our Technology Solutions segment in the accompanying condensed consolidated statement of operations. Most of the goodwill impairment was not deductible for income tax purposes. Refer to Financial Note 5, “Divestitures” for more information on the sale of the EIS business. Refer to Financial Note 15, “Fair Value Measurements” for more information on these nonrecurring fair value measurements.

Goodwill Impairment Charges

Goodwill impairment testing is conducted at the reporting unit level, which is generally defined as an operating segment or at one level below an operating segment (also known as a component), for which discrete financial information is available and segment management regularly reviews the operating results of that reporting unit. We evaluate goodwill for impairment on an annual basis as of January 1 each year and at an interim date, if indicators of impairment exist.

McKesson Europe AG (“McKesson Europe”)

During the second quarter of 2018, our McKesson Europe reporting unit within our Distribution Solutions segment experienced a decline in its estimated future cash flows, primarily in our United Kingdom (“U.K.”) retail business, driven by significant government reimbursement reductions affecting retail pharmacy economics across the U.K. market. Accordingly, we performed an interim one-step goodwill impairment test in accordance with the amended goodwill guidance for this reporting unit prior to our annual impairment test.

As a result of the test, the estimated fair value of this reporting unit was determined to be lower than the carrying value. In the second quarter of 2018, we recorded a non-cash pre-tax and after-tax charge of $350 million to impair the carrying value of this reporting unit’s goodwill under the caption, “Goodwill Impairment Charges” in the accompanying condensed consolidated statement of operations. There were no tax benefits associated with the goodwill impairment charge. The fair value of the reporting unit was determined using a combination of an income approach based on a discounted cash flow (“DCF”) model and a market approach based on guideline public companies’ revenues and earnings before interest, tax, depreciation and amortization multiples. Fair value estimates result from a complex series of judgments about future events and uncertainties and rely heavily on estimates and assumptions that have been deemed reasonable by management as of the measurement date. Any changes in key assumptions, including failure to improve operations of certain retail pharmacy stores, additional government reimbursement reductions, deterioration in the financial market, an increase in interest rates or an increase in the cost of equity financing by market participants within the industry, or other unanticipated events and circumstances, may affect such estimates. Fair value assessments of the reporting unit are considered a Level 3 measurement due to the significance of unobservable inputs developed using company specific information. The discount rate and terminal growth rate used in our 2018 second quarter impairment testing for this reporting unit were 7.5% and 1.25% compared to 7.0% and 1.5% in our 2017 annual impairment test. No additional significant indicators of goodwill impairment exist during the third quarter of 2018. At December 31, 2017, the McKesson Europe reporting unit had a remaining goodwill balance of $2,692 million.

Other risks, expenses and future developments that we were unable to anticipate as of the interim testing date in the second quarter of 2018 may require us to further revise the future projected cash flows, which could adversely affect the fair value of this reporting unit in future periods. As a result, we may be required to record additional impairment charges. Refer to Financial Note 4, “Restructuring and Asset Impairment Charges,” for more information.

Enterprise Information Solutions

In conjunction with the Healthcare Technology Net Asset Exchange, we evaluated strategic options for our EIS business, which was a reporting unit within our Technology Solutions segment during 2017. In the second quarter of 2017, we recorded a non-cash pre-tax charge of $290 million ($282 million after-tax) to impair the carrying value of this reporting unit’s goodwill. The impairment primarily resulted from a decline in estimated cash flows. The amount of goodwill impairment for the EIS business was determined under the former accounting guidance on goodwill impairment testing, and computed as the excess of the carrying value of the reporting unit’s goodwill over the implied fair value of its goodwill. The charge was recorded under the caption, “Goodwill Impairment Charges,” within our Technology Solutions segment in the accompanying condensed consolidated statement of operations. Most of the goodwill impairment was not deductible for income tax purposes. Refer to Financial Note 5, “Divestitures” for more information on the sale of the EIS business.

Refer to Financial Note 15, “Fair Value Measurements” for more information on these nonrecurring fair value measurements.