Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Financial instruments owned:
Total assets measured at fair value	$ 330	$ 691
Fiduciary Assets:
Total fiduciary assets measured at fair value	201	582
Liabilities:
Total liabilities measured at fair value	377	352
Identical Assets (Level 1)
Financial instruments owned:
Total assets measured at fair value	314	678
Fiduciary Assets:
Total fiduciary assets measured at fair value	201	582
Liabilities:
Total liabilities measured at fair value	0	0
Observable Inputs (Level 2)
Financial instruments owned:
Total assets measured at fair value	13	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	3	5
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	377	352
US treasury bills
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	55
US treasury bills | Identical Assets (Level 1)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	55
US treasury bills | Observable Inputs (Level 2)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
US treasury bills | Unobservable Inputs (Level 3)
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Money market funds
Fiduciary Assets:
Total fiduciary assets measured at fair value	201	527
Money market funds | Identical Assets (Level 1)
Fiduciary Assets:
Total fiduciary assets measured at fair value	201	527
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
Other Assets
Financial instruments owned:
Exchange traded equity securities	6	61
Mutual funds	162	192
Other equity investment	13	8
Other Assets | Identical Assets (Level 1)
Financial instruments owned:
Exchange traded equity securities	6	61
Mutual funds	162	192
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	13	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	146	425
Cash and Cash Equivalents | Identical Assets (Level 1)
Financial instruments owned:
Money market funds	146	425
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	3	5
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	3	5
Accounts Payable and Accrued Liabilities and Other Liabilities
Liabilities:
Contingent purchase consideration liability	377	352
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	$ 377	$ 352