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Investment in Change Healthcare Joint Venture (Details) - USD ($) |  |  | 3 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 09, 2020 | Jul. 01, 2019 | Mar. 31, 2020 | Sep. 30, 2019 | Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019 | Mar. 10, 2020 | Apr. 01, 2019 | Mar. 31, 2018 | Mar. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Shares distributed in split-off (shares) | 176,000,000.0 |  |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) |  |  | $ 0.01 |  | $ 0.01 | $ 0.01 |  |  |  |  |
Net gain from sale of equity method investment, pre-tax |  |  |  |  | $ 0 | $ 0 | $ 56,000,000 |  |  |  |
Cumulative effect adjustment |  |  | $ 5,309,000,000 |  | 175,000,000 | 5,309,000,000 | 8,287,000,000 |  |  | $ 10,057,000,000 |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  | $ (48,000,000) | (36,000,000) | (43,000,000) |  |  |  |
Opening retained earnings adjustments: adoption of new accounting standard |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment |  |  | (13,000,000) |  |  | (13,000,000) | 11,000,000 |  |  | 154,000,000 |
Tax Receivable Agreement (“TRA”) |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percentage of net cash tax savings realized or deemed realized under TRA (percent) |  |  |  |  | 85.00% |  |  |  |  |  |
Due from Related Parties |  |  | 0 |  | $ 0 | 0 |  |  |  |  |
Separation of Change Healthcare JV |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Shares distributed in split-off (shares) | 176,000,000.0 |  |  |  |  |  |  |  |  |  |
Shares of common stock exchanged (shares) | 15,400,000 |  |  |  |  |  |  |  |  |  |
Number of shares converted into per share converted (shares) |  |  |  |  |  |  |  | 1 |  |  |
Common stock, par value (in dollars per share) |  |  |  |  |  |  |  | $ 0.001 |  |  |
Retained Earnings |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment |  |  | 13,022,000,000 |  | 8,202,000,000 | 13,022,000,000 | 12,409,000,000 |  |  | 12,986,000,000 |
Retained Earnings | Opening retained earnings adjustments: adoption of new accounting standard |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment |  |  | (13,000,000) |  |  | (13,000,000) | 11,000,000 |  | $ 69,000,000 | $ 154,000,000 |
Prescription Technology Solutions | Tax Receivable Agreement (“TRA”) | Change Healthcare |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  | 90,000,000 |  |  |  |
Noncurrent liability |  |  | 0 |  | $ 0 | 0 |  |  |  |  |
Change Healthcare |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net gain from sale of equity method investment, pre-tax | $ 414,000,000 |  |  |  |  |  |  |  |  |  |
Change Healthcare, Inc. |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net cash proceeds from IPO |  | $ 888,000,000 |  |  |  |  |  |  |  |  |
Proceeds from other security offering |  | $ 279,000,000 |  |  |  |  |  |  |  |  |
Change Healthcare, Inc. | IPO |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Offering price (in usd per share) |  | $ 13 |  |  |  |  |  |  |  |  |
Change Healthcare, Inc. | Change Healthcare |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  | 41.50% |  |  |  |  |  |  |  |  |
Contributions made in exchange for additional membership interests |  | $ 609,000,000 |  |  |  |  |  |  |  |  |
Corporate Joint Venture |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  |  |  |  |  |  |  |  |  |  | 70.00%
Pre-tax dilution loss |  |  |  | $ 246,000,000 |  |  |  |  |  |  |
Corporate Joint Venture | Transition Services Agreements (“TSA”) |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total fees charged under the TSA |  |  |  |  |  | 22,000,000 | 60,000,000 |  |  |  |
Corporate Joint Venture | Change Healthcare |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  | 58.50% |  |  |  |  |  |  |  |  |
Pre-tax dilution loss |  |  |  |  |  | 246,000,000 |  |  |  |  |
Pre-tax other-than-temporary impairment |  |  |  | $ 1,200,000,000 |  | 1,200,000,000 |  |  |  |  |
Net gain from sale of equity method investment, pre-tax |  |  | $ 414,000,000 |  |  |  |  |  |  |  |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  |  | $ 119,000,000 | 194,000,000 |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  | $ (90,000,000) |  |  |  |
Corporate Joint Venture | Change Healthcare | ASU 2014-09 | Retained Earnings | Opening retained earnings adjustments: adoption of new accounting standard |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment |  |  |  |  |  |  |  |  | $ 80,000,000 |  |
Corporate Joint Venture | Change Healthcare, Inc. |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  |  |  |  |  |  |  |  |  |  | 30.00%

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http://asc.fasb.org/extlink&oid=115929471&loc=d3e21914-107793 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22644-107794 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4568740-111683 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4I -URI http://asc.fasb.org/extlink&oid=120409616&loc=SL4590271-111686 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (f) -URI 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