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Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Financial instruments owned: |  |  |
Exchange traded equity securities |  | $ 81 | $ 89
Total assets measured at fair value |  | 16,176 | 14,332
Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Total assets measured at fair value |  | 382 | 252
Fiduciary Assets: |  |  |
Fiduciary assets |  | 111 | 90
Liabilities: |  |  |
Total liabilities measured at fair value |  | 189 | 241
Identical Assets (Level 1) |  |  |
Financial instruments owned: |  |  |
Exchange traded equity securities |  | 81 | 89
Total assets measured at fair value |  | 2,586 | 2,618
Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Total assets measured at fair value |  | 382 | 252
Fiduciary Assets: |  |  |
Fiduciary assets |  | 111 | 90
Liabilities: |  |  |
Total liabilities measured at fair value |  | 0 | 0
Observable Inputs (Level 2) |  |  |
Financial instruments owned: |  |  |
Exchange traded equity securities |  | 0 | 0
Total assets measured at fair value |  | 4,238 | 3,452
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Total assets measured at fair value |  | 0 | 0
Fiduciary Assets: |  |  |
Fiduciary assets |  | 0 | 0
Liabilities: |  |  |
Total liabilities measured at fair value |  | 0 | 0
Unobservable Inputs (Level 3) |  |  |
Financial instruments owned: |  |  |
Exchange traded equity securities |  | 0 | 0
Total assets measured at fair value |  | 372 | 323
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Total assets measured at fair value |  | 0 | 0
Fiduciary Assets: |  |  |
Fiduciary assets |  | 0 | 0
Liabilities: |  |  |
Total liabilities measured at fair value |  | 189 | 241
Other Assets | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Mutual funds | [1] | 158 | 141
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Mutual funds | [1] | 158 | 141
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Mutual funds |  | 0 | 0
Other Assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Mutual funds |  | 0 | 0
Cash and Cash Equivalents | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Money market funds | [2] | 143 | 22
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |
Financial instruments owned: |  |  |
Money market funds | [2] | 143 | 22
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 | [3] | 189 | 241
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 | [3] | 189 | 241
Money Market Funds | Fair Value, Measurements, Recurring |  |  |
Fiduciary Assets: |  |  |
Fiduciary assets |  | 111 | 90
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |
Fiduciary Assets: |  |  |
Fiduciary assets |  | 111 | 90
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
[1] | Included in other assets in the consolidated balance sheets.
[2] | Included in cash and cash equivalents in the consolidated balance sheets.
[3] | ncluded in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.

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