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Commitments and Contingencies - Narrative (Details) £ in Millions, $ in Millions |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2018 USD ($) | Jan. 26, 2018 USD ($) | Oct. 03, 2017 NZD ($) | Dec. 20, 2016 GBP (£) | Jun. 29, 2015 NZD ($) | Sep. 14, 2010 USD ($) | Aug. 31, 2015 USD ($) | Mar. 31, 2015 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2017 USD ($) | Apr. 30, 2014 GBP (£)
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 2,561,000,000 | $ 2,368,000,000 | $ 5,651,000,000 | $ 4,749,000,000 |  |  |
Maximum potential funding under commitments |  |  |  |  |  |  |  |  | 89,000,000 |  | 89,000,000 |  |  | $ 95,000,000 |
Letters of credit outstanding |  |  |  |  |  |  |  |  | 93,000,000 |  | 93,000,000 |  |  | $ 96,000,000 |
Potential Claim for Pension Advisory Services |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | 60,000,000 |  | 60,000,000 |  |  |  | £ 45
Opry Mills Mall Limited Partnership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Damages sought |  |  |  |  |  | $ 200,000,000 |  |  |  |  |  |  |  |  |
Amount of coverage for damages contended by the insurers |  |  |  |  |  | 50,000,000 |  |  |  |  |  |  |  |  |
Difference amount of damages sought by the client |  |  |  |  |  | $ 150,000,000 |  |  |  |  |  |  |  |  |
Damages awarded |  | $ 50,000,000 |  |  |  |  | $ 204,000,000 | $ 200,000,000 |  |  |  |  |  |  |
Pending Litigation | Trustees Of Gleeds Pension Fund 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | 93,000,000 |  | 93,000,000 |  |  |  |
Damages sought | £ |  |  |  | £ 70 |  |  |  |  |  |  |  |  |  |  |
Pending Litigation | Lyttleton Port Company Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Damages sought | $ 126,000,000 |  |  |  | $ 184 |  |  |  |  |  |  |  |  |  |
Pending Litigation | Christchurch City Council |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Damages sought | $ 362,000,000 |  | $ 528 |  |  |  |  |  |  |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | 0 |  | 0 |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  |  | 100,000,000 |  | 100,000,000 |  |  |  |
Aviation and Aerospace Broking Industry |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |
Discontinued Operations, Disposed of by Sale | Tempo Business | Property Lease Guarantee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor obligations, current carrying value |  |  |  |  |  |  |  |  | 20,000,000 |  | 20,000,000 |  |  |  |
Loss contingency accrual payments |  |  |  |  |  |  |  |  | 0 |  | 0 |  |  |  |
Maximum potential funding under commitments |  |  |  |  |  |  |  |  | 93,000,000 |  | 93,000,000 |  |  |  |
Discontinued Operations, Disposed of by Sale | Tempo Business | Performance Guarantee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal, Guarantees and Indemnifications |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor obligations, current carrying value |  |  |  |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  |  |  |
Loss contingency accrual payments |  |  |  |  |  |  |  |  | 0 |  | 0 |  |  |  |
Maximum potential funding under commitments |  |  |  |  |  |  |  |  | $ 200,000,000 |  | $ 200,000,000 |  |  |  |

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