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Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Financial instruments owned: |  |
Exchange traded equity securities | $ 72 | $ 19
Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 816 | 317
Fiduciary Assets: |  |
Fiduciary assets | 134 | 400
Liabilities: |  |
Total liabilities measured at fair value | 233 | 225
Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 744 | 225
Fiduciary Assets: |  |
Fiduciary assets | 134 | 400
Liabilities: |  |
Total liabilities measured at fair value | 0 | 0
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 8 | 8
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Liabilities: |  |
Total liabilities measured at fair value | 0 | 0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 64 | 84
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Liabilities: |  |
Total liabilities measured at fair value | 233 | 225
US Treasury Bills | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 55 | 40
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 55 | 40
US Treasury Bills | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
US Treasury Bills | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Money Market Funds | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 79 | 360
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 79 | 360
Money Market Funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Money Market Funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Other Assets | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 59 | 4
Mutual funds | 155 | 166
Other equity investments | 8 | 8
Contingent purchase consideration asset | 64 | 84
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 59 | 4
Mutual funds | 155 | 166
Other equity investments | 0 | 0
Contingent purchase consideration asset | 0 | 0
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 0 | 0
Mutual funds | 0 | 0
Other equity investments | 8 | 8
Contingent purchase consideration asset | 0 | 0
Other Assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 0 | 0
Mutual funds | 0 | 0
Other equity investments | 0 | 0
Contingent purchase consideration asset | 64 | 84
Cash and Cash Equivalents | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 530 | 55
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 530 | 55
Cash and Cash Equivalents | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 0 | 0
Cash and Cash Equivalents | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 0 | 0
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liability | 233 | 225
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liability | 0 | 0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liability | 0 | 0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liability | $ 233 | $ 225

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