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Investment in Change Healthcare Joint Venture - Net Gain on Split-off of Change Healthcare JV (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |  | 12 Months Ended
--- | --- | ---
Mar. 09, 2020 | Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018
Schedule of Equity Method Investments [Line Items] |  |  |  |
Estimated net gain on split-off of the Change Healthcare JV |  | $ 0 | $ 56 | $ 43
Change Healthcare |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Fair value of McKesson common stock accepted (15,426,537 shares at $131.97 per share on March 9, 2020) | $ 2,036 |  |  |
Investment in the Change Healthcare JV at exchange date | (2,096) |  |  |
Reversal of deferred tax liability | 521 |  |  |
Release of accumulated other comprehensive attributable to the joint venture | (24) |  |  |
Transaction costs incurred | (23) |  |  |
Estimated net gain on split-off of the Change Healthcare JV | $ 414 |  |  |
Separation of Change Healthcare JV |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Shares repurchased (in shares) | 15.4 |  |  |
Price paid per share (in dollars per share) | $ 131.97 |  |  |

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