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Fair Value Measurements (Narrative) (Details) $ / shares in Units, £ in Billions |  | 12 Months Ended |
--- | --- | --- | ---
Sep. 18, 2018 GBP (£) | Dec. 31, 2018 USD ($) $ / shares | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2018 R / shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Total consideration |  | $ 1,040,000,000 | $ 777,000,000 |  |
Assets transferred between Level 1 and Level 2 |  | 0 |  |  |
Net charge for adjustments related to acquisitions |  | 32,000,000 | 3,000,000 | $ 9,000,000 |
Increase in fair value of contingent consideration due to 5% increase in projections |  | 43,000,000 |  |  |
Decrease in fair value of contingent consideration due to 5% decrease in projections |  | 35,000,000 |  |  |
Equity method investments |  | $ 287,000,000 | 405,000,000 |  |
Minimum |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Revenue target period (in years) |  | 2 years |  |  |
Maximum |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Revenue target period (in years) |  | 4 years |  |  |
Private Insurance and Consulting |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Equity method investments |  | $ 61,000,000 | 63,000,000 |  |
Private Equity Funds |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Equity method investments |  | $ 82,000,000 | $ 76,000,000 |  |
Money Market Funds |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Share price (Rand) | $ / shares |  | $ 1.00 |  |  |
Jardine Lloyd Thompson Group plc |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Total consideration | £ | £ 5.2 |  |  |  |
Alexander Forbes Group Holdings Limited |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Share price (Rand) | R / shares |  |  |  |  | R 5.14
Equity method investments |  | $ 144,000,000 |  |  |
Treasury Lock | Jardine Lloyd Thompson Group plc |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Derivative hedge, asset |  | $ 2,000,000,000 |  |  |

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