Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financial instruments owned:
Total assets measured at fair value	$ 691	$ 908
Fiduciary Assets:
Total fiduciary assets measured at fair value	582	323
Liabilities:
Total liabilities measured at fair value	352	243
Identical Assets (Level 1)
Financial instruments owned:
Total assets measured at fair value	678	832
Fiduciary Assets:
Total fiduciary assets measured at fair value	582	323
Liabilities:
Total liabilities measured at fair value	0	0
Observable Inputs (Level 2)
Financial instruments owned:
Total assets measured at fair value	8	8
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	0	0
Unobservable Inputs (Level 3)
Financial instruments owned:
Total assets measured at fair value	5	68
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	352	243
Money market funds
Fiduciary Assets:
Total fiduciary assets measured at fair value	527	173
Money market funds | Identical Assets (Level 1)
Fiduciary Assets:
Total fiduciary assets measured at fair value	527	173
Money market funds | Observable Inputs (Level 2)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Money market funds | Unobservable Inputs (Level 3)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
U.S. Treasury Bills(e)
Fiduciary Assets:
Total fiduciary assets measured at fair value	55	150
U.S. Treasury Bills(e) | Identical Assets (Level 1)
Fiduciary Assets:
Total fiduciary assets measured at fair value	55	150
U.S. Treasury Bills(e) | Observable Inputs (Level 2)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
U.S. Treasury Bills(e) | Unobservable Inputs (Level 3)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Other Assets
Financial instruments owned:
Exchange traded equity securities	61	59
Mutual funds	192	186
Other equity investment	8	8
Other Assets | Identical Assets (Level 1)
Financial instruments owned:
Exchange traded equity securities	61	59
Mutual funds	192	186
Other equity investment	0	0
Other Assets | Observable Inputs (Level 2)
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Other equity investment	8	8
Other Assets | Unobservable Inputs (Level 3)
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Other equity investment	0	0
Cash and Cash Equivalents
Financial instruments owned:
Money market funds	425	587
Cash and Cash Equivalents | Identical Assets (Level 1)
Financial instruments owned:
Money market funds	425	587
Cash and Cash Equivalents | Observable Inputs (Level 2)
Financial instruments owned:
Money market funds	0	0
Cash and Cash Equivalents | Unobservable Inputs (Level 3)
Financial instruments owned:
Money market funds	0	0
Other Receivables
Financial instruments owned:
Contingent purchase consideration asset	5	68
Other Receivables | Identical Assets (Level 1)
Financial instruments owned:
Contingent purchase consideration asset	0	0
Other Receivables | Observable Inputs (Level 2)
Financial instruments owned:
Contingent purchase consideration asset	0	0
Other Receivables | Unobservable Inputs (Level 3)
Financial instruments owned:
Contingent purchase consideration asset	5	68
Accounts Payable and Accrued Liabilities and Other Liabilities
Liabilities:
Contingent purchase consideration liability	352	243
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1)
Liabilities:
Contingent purchase consideration liability	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2)
Liabilities:
Contingent purchase consideration liability	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3)
Liabilities:
Contingent purchase consideration liability	$ 352	$ 243