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Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended | 30 Months Ended
--- | --- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018 | Dec. 31, 2021
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | $ 112 | $ 65 | $ 72
Amounts Accrued |  | 44 | 161 |
Cash Paid |  | (82) | (114) |
Other |  | (2) | 0 |
Liability at end of period | $ 72 | 72 | 112 |
Severance |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 73 | 15 | 37
Amounts Accrued |  | 38 | 137 |
Cash Paid |  | (73) | (77) |
Other |  | (1) | (2) |
Liability at end of period | 37 | 37 | 73 |
Future rent under non-cancelable leases and other costs |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 39 | 50 | 35
Amounts Accrued |  | 6 | 24 |
Cash Paid |  | (9) | (37) |
Other |  | (1) | 2 |
Liability at end of period | 35 | 35 | 39 |
Risk and Insurance Services Segment | Severance and Consulting Costs |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | 2 | 7 |  |
Mercer Consulting Group | Severance and Consulting Costs |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | 22 | 32 |  |
Jardine Lloyd Thompson Group plc |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 0 |  | 74
Amounts Accrued |  | 134 |  |
Cash Paid |  | (60) |  |
Other |  | 0 |  |
Liability at end of period | 74 | 74 | 0 |
Jardine Lloyd Thompson Group plc | Severance |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 0 |  | 46
Amounts Accrued |  | 73 |  |
Cash Paid |  | (27) |  |
Other |  | 0 |  |
Liability at end of period | 46 | 46 | 0 |
Jardine Lloyd Thompson Group plc | Acquisition Related |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | 98 | 134 |  |
Jardine Lloyd Thompson Group plc | Real estate related costs |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 0 |  | 0
Amounts Accrued |  | 0 |  |
Cash Paid |  | 0 |  |
Other |  | 0 |  |
Liability at end of period | 0 | 0 | 0 |
Jardine Lloyd Thompson Group plc | Consulting and other outside services |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability at beginning of period |  | 0 |  | 28
Amounts Accrued |  | 61 |  |
Cash Paid |  | (33) |  |
Other |  | 0 |  |
Liability at end of period | 28 | 28 | $ 0 |
Jardine Lloyd Thompson Group plc | Risk and Insurance Services Segment | Acquisition Related |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | 75 | 95 |  |
Jardine Lloyd Thompson Group plc | Consulting Segment | Acquisition Related |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | 5 | 5 |  |
Corporate, Non-Segment | Severance and Future Rent Under Non-Cancelable Leases and Other Costs |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued |  | 5 |  |
Corporate, Non-Segment | Jardine Lloyd Thompson Group plc | Acquisition Related |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued | $ 18 | $ 34 |  |
Scenario, Forecast | Jardine Lloyd Thompson Group plc | Acquisition Related |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Amounts Accrued |  |  |  | $ 375

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