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Derivatives - Narrative (Details) £ in Billions |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 18, 2018 GBP (£) | Jan. 31, 2019 USD ($) | Mar. 31, 2019 USD ($) | Sep. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jun. 29, 2019 | Mar. 30, 2019
Derivative [Line Items] |  |  |  |  |  |  |  |
Total consideration |  |  |  |  | $ 1,040,000,000 | $ 777,000,000 |  |
Exchange rate |  |  |  | 0.0343 |  |  |  |
Foreign Exchange Forward |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Unrealized loss |  |  |  | $ 325,000,000 |  |  |  |
Jardine Lloyd Thompson Group plc |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Total consideration | £ | £ 5.2 |  |  |  |  |  |  |
Jardine Lloyd Thompson Group plc | Treasury Lock |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Unrealized loss |  |  |  |  | 116,000,000 |  |  |
Derivative hedge, asset |  |  |  |  | $ 2,000,000,000 |  |  |
Forecast |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Exchange rate |  |  |  |  |  |  | 0.000145 | 0.00016
Forecast | Treasury Lock |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Payments for derivative instrument |  |  | $ 6,000,000 |  |  |  |  |
Subsequent Event | Treasury Lock |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Payments for derivative instrument |  | $ 122,000,000 |  |  |  |  |  |
Senior Notes | Subsequent Event |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |
Debt instrument, amount |  | $ 5,000,000,000 |  |  |  |  |  |

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