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Fair Value Measurements (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions | 3 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2017 USD ($) $ / shares shares | Mar. 31, 2016 USD ($) | Mar. 31, 2017 ZAR / shares | Jan. 31, 2017 ZAR / shares | Dec. 31, 2016 USD ($) | Jan. 31, 2016 ZAR / shares | Feb. 24, 2015 USD ($) | Dec. 31, 2014 ZAR / shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Adjustments to acquisition related contingent consideration liability | $ (16) |  |  |  |  |  |  |
Increase in fair value of contingent consideration due to 5% increase in projections | 22 |  |  |  |  |  |  |
Decrease in fair value of contingent consideration due to 5% decrease in projections | (22) |  |  |  |  |  |  |
Carrying value of investment | 426 |  |  |  | $ 389 |  |  |
Unrealized investment gains (losses) | $ (5) | $ 0 |  |  |  |  |  |
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 Equity Funds, Foreign |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Carrying value of investment | $ 72 |  |  |  | $ 79 |  |  |
Alexander Forbes Group Holdings Limited |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Share price (Rand) | ZAR / shares |  |  | ZAR 6.43 |  |  |  |  | ZAR 7.50
Carrying value of investment | $ 289 |  |  |  |  |  |  |
Percentage of ownership in equity investment | 33.00% |  |  |  |  |  |  |
Investment shares owned | shares | 443 |  |  |  |  |  |  |
Market value of investment | $ 229 |  |  |  |  |  |  |
Alexander Forbes Group Holdings Limited | Minimum |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Share price (Rand) | ZAR / shares |  |  |  |  |  | ZAR 6.38 |  |
Alexander Forbes Group Holdings Limited | Maximum |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Share price (Rand) | ZAR / shares |  |  |  | ZAR 7.89 |  |  |  |
Mercer Consulting Group | Benefitfocus |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Market value of investment | $ 79 |  |  |  |  |  |  |
Percentage of business interest acquired |  |  |  |  |  |  | 9.90% |
Total consideration |  |  |  |  |  |  | $ 75 |
Money Market Funds |  |  |  |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |  |  |  |
Share price (Rand) | $ / shares | $ 1.00 |  |  |  |  |  |  |

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