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Stockholders' Equity (Deficit) - Schedule of Other Comprehensive Income (Loss), Net of Tax (Details) € in Millions, £ in Millions, $ in Millions | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2020 EUR (€) | Dec. 31, 2020 GBP (£) | Mar. 31, 2020 EUR (€) | Dec. 31, 2019 EUR (€) | Dec. 31, 2019 GBP (£) | Sep. 30, 2019 GBP (£)
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | $ 50 | $ 45 | $ 90 | $ 86 |  |  |  |  |  |
Reclassified to income statement, net of income tax expense | 69 | 6 | 71 | 98 |  |  |  |  |  |
Other comprehensive income (loss) | 119 | 51 | 161 | 184 |  |  |  |  |  |
Foreign currency translation adjustments, tax | 0 | 0 | 0 | 0 |  |  |  |  |  |
Reclassified to income statement, tax | 0 | 0 | 0 | 0 |  |  |  |  |  |
Unrealized gains (loss) on cash flow hedges arising during period, tax | 2 | 3 | 6 | (7) |  |  |  |  |  |
Net actuarial loss and prior service cost arising during the period, tax | 0 | 0 | 0 | 1 |  |  |  |  |  |
Amortization of actuarial (gain) loss and prior service costs, tax | 2 | 0 | 1 | 0 |  |  |  |  |  |
Foreign currency translation adjustments and other, tax | 0 | 0 | 0 | 0 |  |  |  |  |  |
Net actuarial gain (losses) attributable to redeemable noncontrolling interest | 5 | (2) | 3 | (1) |  |  |  |  |  |
Foreign Currency Translation Adjustments, Net of Tax |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | 156 | 101 | 363 | 57 |  |  |  |  |  |
Reclassified to income statement, net of income tax expense | 47 | 0 | 47 | 0 |  |  |  |  |  |
Other comprehensive income (loss) | 203 | 101 | 410 | 57 |  |  |  |  |  |
Translation gain (loss) attributable to redeemable noncontrolling interest | 20 | 12 | (41) | (1) |  |  |  |  |  |
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | (96) | (58) | (229) | (2) |  |  |  |  |  |
Reclassified to income statement, net of income tax expense | 0 | 0 | 0 | 0 |  |  |  |  |  |
Other comprehensive income (loss) | (96) | (58) | (229) | (2) |  |  |  |  |  |
Unrealized gains (losses) on net investment hedges arising during period, tax | 33 | 21 | 80 | 1 |  |  |  |  |  |
Reclassified to income statement, tax | 0 | 0 | 0 | 0 |  |  |  |  |  |
Gain (loss) from net investment hedges recorded within other comprehensive income | 0 |  | (1) |  |  |  |  |  |  |
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | (12) | 8 | (36) | 33 |  |  |  |  |  |
Reclassified to income statement, net of income tax expense | 0 | 0 | 0 | 0 |  |  |  |  |  |
Other comprehensive income (loss) | (12) | 8 | (36) | 33 |  |  |  |  |  |
Reclassified to income statement, tax | 0 | 0 | 0 | 0 |  |  |  |  |  |
Net actuarial loss and prior servicecost arising during the period, net of income tax benefit |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | 0 | 0 | 0 | (3) |  |  |  |  |  |
Amortization of actuarial loss, prior service cost and transition obligation, net of income tax expense |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | (2) | (2) | 0 | 0 |  |  |  |  |  |
Foreign currency translation adjustments and other, net of income tax expense |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss) before reclassifications | 2 | (6) | (8) | 1 |  |  |  |  |  |
Changes in retirement-related benefit plans |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Reclassified to income statement, net of income tax expense | 24 | 8 | 24 | 98 |  |  |  |  |  |
Other comprehensive income (loss) | 24 | 0 | 16 | 96 |  |  |  |  |  |
Reclassified to income statement, tax | 9 | 3 | 9 | 35 |  |  |  |  |  |
Euro Denominated Notes | Term Loan |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt outstanding | € |  |  |  |  |  |  |  | € 1,700 |  |
British Pound Sterling Denominated Notes | Term Loan |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt outstanding | £ |  |  |  |  |  | £ 450 |  |  | £ 450 | £ 450
Net Investment Hedging | Euro Denominated Notes | Term Loan |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt outstanding | € |  |  |  |  | € 1,700 |  | € 1,700 |  |  |
Derivatives designated for hedge accounting |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Gain (loss) from net investment hedges recorded within other comprehensive income | (84) | (59) | (201) | 8 |  |  |  |  |  |
Derivatives designated for hedge accounting | Net Investment Hedging |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |
Derivatives used in net investment hedge, gains (losses) gross | $ (45) | $ (20) | $ (108) | $ (11) |  |  |  |  |  |

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