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Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Financial instruments owned: |  |
Exchange traded equity securities | $ 19 | $ 16
Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 544 | 790
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 65 | 180
Liabilities: |  |
Total liabilities measured at fair value | 121 | 252
Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Total assets measured at fair value | 544 | 789
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 65 | 180
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 | 0 | 0
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 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 | 0 | 1
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 0 | 0
Liabilities: |  |
Total liabilities measured at fair value | 121 | 252
Money market funds | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 65 | 180
Money market funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 65 | 180
Money market funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 0 | 0
Money market funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Fiduciary Assets: |  |
Total fiduciary assets measured at fair value | 0 | 0
Other Assets | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 8 | 5
Mutual funds | 182 | 178
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 8 | 5
Mutual funds | 182 | 178
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Exchange traded equity securities | 0 | 0
Mutual funds | 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
Money market funds | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 354 | 606
Money market funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 354 | 606
Money market funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 0 | 0
Money market funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Money market funds | 0 | 0
Contingent purchase consideration assets | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration assets | 0 | 1
Contingent purchase consideration assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration assets | 0 | 0
Contingent purchase consideration assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration assets | 0 | 0
Contingent purchase consideration assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Financial instruments owned: |  |
Contingent purchase consideration assets | 0 | 1
Contingent purchase consideration liabilities | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liabilities | 121 | 252
Contingent purchase consideration liabilities | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liabilities | 0 | 0
Contingent purchase consideration liabilities | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liabilities | 0 | 0
Contingent purchase consideration liabilities | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |
Liabilities: |  |
Contingent purchase consideration liabilities | $ 121 | $ 252

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