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Hedging Activities - Narrative (Details) $ in Millions | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 EUR (€) | Jun. 30, 2018 GBP (£) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 GBP (£) | Mar. 31, 2018 USD ($) | Jun. 30, 2017 EUR (€)
Derivative [Line Items] |  |  |  |  |  |  |  |
Long-term debt outstanding |  |  |  |  | $ 7,719 |  | $ 7,880 |
Derivatives used in Net investment hedge, gains (loss) gross | $ 161 | $ (114) |  |  |  |  |  |
Gains (losses) from cash flow hedges | 0 | 14 |  |  |  |  |  |
Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Gains (losses) from cash flow hedges |  | $ (14) |  |  |  |  |  |
Foreign Exchange Contract | Derivatives not Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional values of financial instruments |  |  |  |  | 39 |  | 29 |
Cross Currency Swap | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional values of financial instruments |  |  |  |  | 3,412 |  | 3,412 |
Forward Contracts | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional values of financial instruments |  |  |  |  | $ 162 |  | $ 162 |
Net Investment Hedging | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Derivatives used in Net investment hedge, gains (loss) gross | $ 34 |  |  |  |  |  |  |
Net Investment Hedging | Cross Currency Swap [Member] | Derivatives Designated for Hedge Accounting |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Notional values of financial instruments | £ |  |  |  |  |  | £ 432,000,000 |  |
Euro Denominated Notes | Term Loan |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Long-term debt outstanding | € |  |  | € 1,950,000,000.00 |  |  |  |  | € 1,200,000,000.00
British Pound Sterling Denominated Notes | Term Loan |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Long-term debt outstanding | £ |  |  |  | £ 450,000,000 |  |  |  |

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