Fair Value Measurements	12 Months Ended
Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a three-level hierarchy that prioritizes the inputs used in determining fair value by their reliability and preferred use, as follows: Level 1 - Valuations based on quoted prices in active markets for identical assets or liabilities. Level 2 - Valuations based on quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data. Level 3 - Valuations based on inputs that are both significant to the fair value measurement and unobservable. At March 31, 2018 and 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. Our long-term debt is carried at amortized cost. The carrying amounts and estimated fair values of these liabilities were $7.9 billion and $8.1 billion at March 31, 2018 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. Assets Measured at Fair Value on a Recurring Basis Cash and cash equivalents included investments in money market funds of $799 million and $478 million at March 31, 2018 and 2017. The fair value of the money market funds was determined by 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 for our marketable securities were not material at March 31, 2018 and 2017. Fair values of our forward foreign currency contracts were determined using observable inputs from available market information. Fair values of our cross-currency swaps were determined using 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 20, “Hedging Activities,” for fair value and other information on our foreign currency derivatives including forward foreign currency contracts and cross-currency swaps. There were no transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy during the years ended March 31, 2018 and 2017. Assets Measured at Fair Value on a Nonrecurring Basis At March 31, 2018, assets measured at fair value on a nonrecurring basis consisted of goodwil, intangible and other long-lived assets for our McKesson Europe and Rexall Health reporting units within our Distribution Solutions segment. At March 31, 2017, assets measured at fair value on a nonrecurring basis primarily consisted of our equity method investment in Change Healthcare (Refer to Financial Note 2, “Healthcare Technology Net Asset Exchange,”) and goodwill for our EIS reporting unit within our Technology Solutions segment. Goodwill Fair value assessments of the reporting unit and the reporting unit's net assets, which are performed for goodwill impairment tests, 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. Refer to Financial Note 3, “Goodwill Impairment Charges,” for more information regarding goodwill impairment charges recorded for these reporting units during 2018 and 2017. Intangible and Other Long-Lived Assets We measure certain intangible and other long-lived assets at fair value on a nonrecurring basis when they are deemed to be other-than-temporarily impaired. 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 $479 million ($443 million after-tax) during 2018 to impair the carrying values of certain long-lived assets including intangible assets and capitalized software assets. We utilized an income approach (DCF method) or a combination of an income approach 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 long-lived assets is considered a Level 3 fair value measurement. Liabilities Measured at Fair Value on a Nonrecurring Basis At March 31, 2018, 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

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a three-level hierarchy that prioritizes the inputs used in determining fair value by their reliability and preferred use, as follows:

Level 1 - Valuations based on quoted prices in active markets for identical assets or liabilities.

Level 2 - Valuations based on quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data.

Level 3 - Valuations based on inputs that are both significant to the fair value measurement and unobservable.

At March 31, 2018 and 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.

Our long-term debt is carried at amortized cost. The carrying amounts and estimated fair values of these liabilities were $7.9 billion and $8.1 billion at March 31, 2018 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.

Assets Measured at Fair Value on a Recurring Basis

Cash and cash equivalents included investments in money market funds of $799 million and $478 million at March 31, 2018 and 2017. The fair value of the money market funds was determined by 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 for our marketable securities were not material at March 31, 2018 and 2017.

Fair values of our forward foreign currency contracts were determined using observable inputs from available market information. Fair values of our cross-currency swaps were determined using 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 20, “Hedging Activities,” for fair value and other information on our foreign currency derivatives including forward foreign currency contracts and cross-currency swaps.

There were no transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy during the years ended March 31, 2018 and 2017.

Assets Measured at Fair Value on a Nonrecurring Basis

At March 31, 2018, assets measured at fair value on a nonrecurring basis consisted of goodwil, intangible and other long-lived assets for our McKesson Europe and Rexall Health reporting units within our Distribution Solutions segment.

At March 31, 2017, assets measured at fair value on a nonrecurring basis primarily consisted of our equity method investment in Change Healthcare (Refer to Financial Note 2, “Healthcare Technology Net Asset Exchange,”) and goodwill for our EIS reporting unit within our Technology Solutions segment.

Goodwill

Fair value assessments of the reporting unit and the reporting unit's net assets, which are performed for goodwill impairment tests, 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.

Refer to Financial Note 3, “Goodwill Impairment Charges,” for more information regarding goodwill impairment charges recorded for these reporting units during 2018 and 2017.

Intangible and Other Long-Lived Assets

We measure certain intangible and other long-lived assets at fair value on a nonrecurring basis when they are deemed to be other-than-temporarily impaired. 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 $479 million ($443 million after-tax) during 2018 to impair the carrying values of certain long-lived assets including intangible assets and capitalized software assets. We utilized an income approach (DCF method) or a combination of an income approach 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 long-lived assets is considered a Level 3 fair value measurement.

Liabilities Measured at Fair Value on a Nonrecurring Basis

At March 31, 2018, 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.