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Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Financial instruments owned: |  |
Exchange traded equity securities | $ 74 | $ 72
Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 382 | 908
Fiduciary Assets: |  |
Fiduciary assets | 241 | 323
Liabilities: |  |
Total liabilities measured at fair value | 233 | 243
Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 308 | 832
Fiduciary Assets: |  |
Fiduciary assets | 241 | 323
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 | 66 | 68
Fiduciary Assets: |  |
Fiduciary assets | 0 | 0
Liabilities: |  |
Total liabilities measured at fair value | 233 | 243
US Treasury Bills | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 150
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 0 | 150
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 | 241 | 173
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Fiduciary assets | 241 | 173
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 | 60 | 59
Mutual funds | 183 | 186
Other equity investments | 8 | 8
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 60 | 59
Mutual funds | 183 | 186
Other equity investments | 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
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
Cash and Cash Equivalents | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 65 | 587
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 65 | 587
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
Other Receivables | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration asset | 66 | 68
Other Receivables | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration asset | 0 | 0
Other Receivables | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration asset | 0 | 0
Other Receivables | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration asset | 66 | 68
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liability | 233 | 243
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 | $ 243

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