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Goodwill and Intangible Assets, Net - Goodwill Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 segment | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) reportingUnit | Mar. 31, 2021 USD ($) segment | Mar. 31, 2021 USD ($) | Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($)
Goodwill [Line Items] |  |  |  |  |  |  |  |
Number of reportable segments | segment | 4 |  |  |  | 4 |  |  |
Goodwill impairment charge |  |  |  |  |  | $ 69 | $ 2 | $ 1,797
Goodwill |  | $ 9,358 |  |  | $ 9,493 | 9,493 | 9,360 | 9,358
International |  |  |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |  |  |
Goodwill impairment charge |  |  |  |  |  | 69 | 2 | 1,776
Goodwill |  | 1,446 |  |  | 1,535 | 1,535 | 1,443 | 1,446
Accumulated goodwill impairment loss |  |  |  |  | 3,600 | 3,600 | $ 3,500 |
International | Europe |  |  |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |  |  |
Goodwill |  |  |  |  | $ 0 | 0 |  |
European Pharmaceutical Solutions |  |  |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |  |  |
Number of reporting units | reportingUnit |  |  |  | 2 |  |  |  |
Retail Pharmacy | International |  |  |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |  |  |
Goodwill impairment charge |  | $ 465 |  | $ 251 |  | $ 69 |  |
Tax charged related to impairment |  |  |  |  |  |  |  | $ 20
Rexall Health | International |  |  |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |  |  |
Goodwill impairment charge |  |  | $ 21 |  |  |  |  |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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