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Claims, Lawsuits, and Other Contingencies - Legal Narrative (Details) £ in Millions, $ in Millions |  |  |  | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2019 NZD ($) | Dec. 31, 2019 USD ($) | Sep. 06, 2018 USD ($) | Jun. 29, 2015 NZD ($) | Dec. 31, 2016 USD ($) | Oct. 20, 2016 GBP (£) | Apr. 30, 2014 GBP (£)
Lyttleton Port Company Limited |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Value of damages sought |  | $ 123,000,000 |  | $ 184 |  |  |
Pending Litigation | Christchurch City Council |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Value of damages sought | $ 528 | 352,000,000 |  |  |  |  |
Minimum |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Estimate of possible loss |  | 0 |  |  |  |  |
Minimum | Pilkington North America, Inc. |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Value of damages sought |  |  | $ 45,000,000 |  |  |  |
Maximum |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Estimate of possible loss |  | 100,000,000 |  |  |  |  |
Maximum | Pilkington North America, Inc. |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Value of damages sought |  |  | 85,000,000 |  |  |  |
Damages awarded |  |  | $ 15,000,000 |  |  |  |
Aviation and Aerospace Broking Industry |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Total revenue |  |  |  |  | $ 100,000,000 |  |
Potential Claim for Pension Advisory Services |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Estimate of possible loss |  | 58,000,000 |  |  |  |  | £ 45
Potential Claim for Pension Advisory Services | Trustees of Gleeds Pension Fund 2016 |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |
Estimate of possible loss |  | $ 91,000,000 |  |  |  | £ 70 |

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