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Hedging Activities - Narrative (Details) £ in Millions, $ in Millions, $ in Billions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2020 EUR (€) | Mar. 31, 2020 CAD ($) | Dec. 31, 2019 EUR (€) | Sep. 30, 2019 GBP (£) | Mar. 31, 2019 EUR (€) | Mar. 31, 2019 GBP (£) | Mar. 31, 2019 CAD ($)
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Total debt outstanding | $ 7,387 | $ 7,595 |  |  |  |  |  |  |  |
Gains (losses) from net investment hedges | 39 | 259 | $ (268) |  |  |  |  |  |  |
Gains recorded in earnings for ineffectiveness of Company's non-derivative hedges | 34 |  |  |  |  |  |  |  |  |
Gains (losses) from fair value hedge recorded in earnings | 6 |  |  |  |  |  |  |  |  |
Gains (losses) recorded in other comprehensive income | 86 | 24 | (30) |  |  |  |  |  |  |
Forward Contracts | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  | 81 |  |  |  |  |  |  |  |
Currency Swap | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | 2,900 | 2,900 |  |  |  |  |  |  |  |
Forward Contracts and Cross Currency Swaps |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Gains (losses) recorded in other comprehensive income | 98 | 28 | (30) |  |  |  |  |  |  |
Foreign Exchange Contract | Derivatives Not Designated for Hedge Accounting | United Kingdom, Pounds |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | 29 | 28 |  |  |  |  |  |  |  |
Forward Contracts to Offset Impact of Ineffectiveness of Net investment Hedges | Derivatives Not Designated for Hedge Accounting |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | € |  |  |  |  |  | € 250,000,000 |  |  |  |
Gains (losses) from contracts not designated as hedges | (44) |  |  |  |  |  |  |  |  |
Net Investment Hedging |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Gains (losses) recorded in other comprehensive income | 76 | $ 53 | $ (7) |  |  |  |  |  |  |
Net Investment Hedging | November 2018 Cross Currency Swaps | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  |  |  | $ 1.5 |  |  |  | £ 932 | $ 1.5
Proceeds from termination of swaps | 84 |  |  |  |  |  |  |  |  |
Settlement gain recorded in earnings | $ 34 |  |  |  |  |  |  |  |  |
Euro Denominated Notes | Notes |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Total debt outstanding | € |  |  |  |  |  | € 250,000,000 |  |  |  |
Euro Denominated Notes | Notes | Net Investment Hedging |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Total debt outstanding | € |  |  |  | € 1,700,000,000 |  |  |  | € 1,950,000,000 |  |
British Pound Sterling Denominated Notes | Notes |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |
Total debt outstanding | £ |  |  |  |  |  |  | £ 450 |  | £ 450 |

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