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Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred |  |  | $ 23 |  | $ 89
Global Information Technology, HR Functions and Future Rent |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred | $ 12 |  | 23 |  |
Jardine Lloyd Thompson Group plc |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred |  |  | 42 |  | $ 251
Jardine Lloyd Thompson Group plc | Acquisition related |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Restructuring and related cost, cost incurred to date | 628 |  | 628 |  |
Costs incurred | 19 | $ 57 | 42 | $ 137 |
Jardine Lloyd Thompson Group plc | Acquisition related | Corporate |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred | 2 |  | 3 |  |
Jardine Lloyd Thompson Group plc | Acquisition related | Risk and Insurance Services Segment |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred | 11 |  | 27 |  |
Jardine Lloyd Thompson Group plc | Acquisition related | Consulting Segment |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Costs incurred | $ 6 |  | $ 12 |  |

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