Fair Value Measurements	9 Months Ended
Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements At December 31, 2017 and March 31, 2017, the carrying amounts of cash, certain cash equivalents, restricted cash, marketable securities, receivables, drafts and accounts payable, short-term borrowings and other current liabilities approximated their estimated fair values because of the short maturity of these financial instruments. The fair value of our commercial paper was determined using quoted prices in active markets for identical liabilities, which are considered to be Level 1 inputs. Assets Measured at Fair Value on a Recurring Basis Our long-term debt is carried at amortized cost. The carrying amounts and estimated fair values of these liabilities were $8.0 billion and $8.5 billion at December 31, 2017, and $8.4 billion and $8.7 billion at March 31, 2017. The estimated fair value of our long-term debt was determined using quoted market prices in a less active market and other observable inputs from available market information, which are considered to be Level 2 inputs, and may not be representative of actual values that could have been realized or that will be realized in the future. Cash and cash equivalents at December 31, 2017 and March 31, 2017 included investments in money market funds of $1,066 million and $478 million, which are reported at fair value. The fair value of the money market funds was determined using quoted prices for identical investments in active markets, which are considered to be Level 1 inputs under the fair value measurements and disclosure guidance. The carrying value of all other cash equivalents approximates their fair value due to their relatively short-term nature. Fair values of our derivatives were determined using quoted market prices of similar instruments in an active market and other observable inputs from available market information. Fair values of our foreign currency swaps were determined using the quoted foreign currency exchange rates and other observable inputs from available market information. These inputs are considered Level 2 under the fair value measurements and disclosure guidance, and may not be representative of actual values that could have been realized or that will be realized in the future. Refer to Financial Note 14, "Hedging Activities," for more information on our derivatives including foreign currency forward contracts and cross currency swaps. There were no transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy during the quarters and nine months ended December 31, 2017 and 2016. Assets Measured at Fair Value on a Nonrecurring Basis At December 31, 2017, assets measured at fair value on a nonrecurring basis consisted of goodwill and intangible assets for our McKesson Europe business within our Distribution Solutions segment, as further discussed below. At March 31, 2017, assets measured at fair value on a nonrecurring basis primarily consisted of goodwill for our EIS business within our Technology Solutions segment. Goodwill As discussed in Financial Note 3, “Goodwill Impairment Charges,” we recorded non-cash pre-tax and after-tax impairment charges of $350 million during the second quarter of 2018 for our McKesson Europe reporting unit within the Distribution Solutions segment, and $290 million ($282 million after-tax) during the second quarter of 2017 for our EIS reporting unit within the Technology Solutions segment. The impairments primarily resulted from a decline in the reporting units’ estimated cash flows. Fair value assessments of the reporting unit and the reporting unit's net assets are considered a Level 3 measurement due to the significance of unobservable inputs developed using company specific information. We considered a market approach as well as an income approach using the DCF model to determine the fair value of the reporting unit. Intangible Assets We measure certain long-lived assets at fair value on a nonrecurring basis when they are deemed to be other-than-temporarily impaired. If the cost of an investment exceeds its fair value, we evaluate, among other factors, our intent to hold the investment, general market conditions, the duration and extent to which the fair value is less than cost and the financial outlook for the industry and location. An impairment charge is recorded when the cost of the asset exceeds its fair value and this condition is determined to be other-than-temporary. As discussed in Financial Note 4, “Restructuring and Asset Impairment Charges,” we recorded non-cash pre-tax charges of $189 million ($157 million after-tax) during the second quarter of 2018 to impair the carrying values of certain long-lived assets including intangible assets. We utilized a combination of an income approach (primarily DCF method) and a market approach for estimating the fair value of intangible assets. The future cash flows used in the analysis are based on internal cash flow projections based on our long-range plans and include significant assumptions by management. Accordingly, the fair value assessment of the intangible assets is considered a Level 3 fair value measurement. Liabilities Measured at Fair Value on a Nonrecurring Basis At December 31, 2017, we remeasured the contingent consideration liability related to our acquisition of CMM at fair value on a nonrecurring basis. Refer to Financial Note 6, “Business Combinations,” for more information on the fair value of the contingent consideration liability. There were no liabilities measured at fair value on a nonrecurring basis at March 31, 2017.

Fair Value Measurements

At December 31, 2017 and March 31, 2017, the carrying amounts of cash, certain cash equivalents, restricted cash, marketable securities, receivables, drafts and accounts payable, short-term borrowings and other current liabilities approximated their estimated fair values because of the short maturity of these financial instruments.

The fair value of our commercial paper was determined using quoted prices in active markets for identical liabilities, which are considered to be Level 1 inputs.

Assets Measured at Fair Value on a Recurring Basis

Our long-term debt is carried at amortized cost. The carrying amounts and estimated fair values of these liabilities were $8.0 billion and $8.5 billion at December 31, 2017, and $8.4 billion and $8.7 billion at March 31, 2017. The estimated fair value of our long-term debt was determined using quoted market prices in a less active market and other observable inputs from available market information, which are considered to be Level 2 inputs, and may not be representative of actual values that could have been realized or that will be realized in the future.

Cash and cash equivalents at December 31, 2017 and March 31, 2017 included investments in money market funds of $1,066 million and $478 million, which are reported at fair value. The fair value of the money market funds was determined using quoted prices for identical investments in active markets, which are considered to be Level 1 inputs under the fair value measurements and disclosure guidance. The carrying value of all other cash equivalents approximates their fair value due to their relatively short-term nature.

Fair values of our derivatives were determined using quoted market prices of similar instruments in an active market and other observable inputs from available market information. Fair values of our foreign currency swaps were determined using the quoted foreign currency exchange rates and other observable inputs from available market information. These inputs are considered Level 2 under the fair value measurements and disclosure guidance, and may not be representative of actual values that could have been realized or that will be realized in the future. Refer to Financial Note 14, "Hedging Activities," for more information on our derivatives including foreign currency forward contracts and cross currency swaps.

There were no transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy during the quarters and nine months ended December 31, 2017 and 2016.

Assets Measured at Fair Value on a Nonrecurring Basis

At December 31, 2017, assets measured at fair value on a nonrecurring basis consisted of goodwill and intangible assets for our McKesson Europe business within our Distribution Solutions segment, as further discussed below.

At March 31, 2017, assets measured at fair value on a nonrecurring basis primarily consisted of goodwill for our EIS business within our Technology Solutions segment.

Goodwill

As discussed in Financial Note 3, “Goodwill Impairment Charges,” we recorded non-cash pre-tax and after-tax impairment charges of $350 million during the second quarter of 2018 for our McKesson Europe reporting unit within the Distribution Solutions segment, and $290 million ($282 million after-tax) during the second quarter of 2017 for our EIS reporting unit within the Technology Solutions segment. The impairments primarily resulted from a decline in the reporting units’ estimated cash flows.

Fair value assessments of the reporting unit and the reporting unit's net assets are considered a Level 3 measurement due to the significance of unobservable inputs developed using company specific information. We considered a market approach as well as an income approach using the DCF model to determine the fair value of the reporting unit.

Intangible Assets

We measure certain long-lived assets at fair value on a nonrecurring basis when they are deemed to be other-than-temporarily impaired. If the cost of an investment exceeds its fair value, we evaluate, among other factors, our intent to hold the investment, general market conditions, the duration and extent to which the fair value is less than cost and the financial outlook for the industry and location. An impairment charge is recorded when the cost of the asset exceeds its fair value and this condition is determined to be other-than-temporary.

As discussed in Financial Note 4, “Restructuring and Asset Impairment Charges,” we recorded non-cash pre-tax charges of $189 million ($157 million after-tax) during the second quarter of 2018 to impair the carrying values of certain long-lived assets including intangible assets. We utilized a combination of an income approach (primarily DCF method) and a market approach for estimating the fair value of intangible assets. The future cash flows used in the analysis are based on internal cash flow projections based on our long-range plans and include significant assumptions by management. Accordingly, the fair value assessment of the intangible assets is considered a Level 3 fair value measurement.

Liabilities Measured at Fair Value on a Nonrecurring Basis

At December 31, 2017, we remeasured the contingent consideration liability related to our acquisition of CMM at fair value on a nonrecurring basis. Refer to Financial Note 6, “Business Combinations,” for more information on the fair value of the contingent consideration liability. There were no liabilities measured at fair value on a nonrecurring basis at March 31, 2017.