Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial instruments owned:
Total assets measured at fair value	$ 512	$ 790
Fiduciary Assets:
Total fiduciary assets measured at fair value	76	180
Liabilities:
Total liabilities measured at fair value	242	252
Identical Assets (Level 1)
Financial instruments owned:
Total assets measured at fair value	511	789
Fiduciary Assets:
Total fiduciary assets measured at fair value	76	180
Liabilities:
Total liabilities measured at fair value	0	0
Observable Inputs (Level 2)
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)
Financial instruments owned:
Total assets measured at fair value	1	1
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Total liabilities measured at fair value	242	252
Money market funds
Fiduciary Assets:
Total fiduciary assets measured at fair value	76	180
Money market funds | Identical Assets (Level 1)
Fiduciary Assets:
Total fiduciary assets measured at fair value	76	180
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	7	5
Mutual funds	183	178
Other Assets | Identical Assets (Level 1)
Financial instruments owned:
Exchange traded equity securities	7	5
Mutual funds	183	178
Other Assets | Observable Inputs (Level 2)
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Other Assets | Unobservable Inputs (Level 3)
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Money market funds
Financial instruments owned:
Money market funds	321	606
Money market funds | Identical Assets (Level 1)
Financial instruments owned:
Money market funds	321	606
Money market funds | Observable Inputs (Level 2)
Financial instruments owned:
Money market funds	0	0
Money market funds | Unobservable Inputs (Level 3)
Financial instruments owned:
Money market funds	0	0
Contingent purchase consideration assets
Financial instruments owned:
Contingent purchase consideration assets	1	1
Contingent purchase consideration assets | Identical Assets (Level 1)
Financial instruments owned:
Contingent purchase consideration assets	0	0
Contingent purchase consideration assets | Observable Inputs (Level 2)
Financial instruments owned:
Contingent purchase consideration assets	0	0
Contingent purchase consideration assets | Unobservable Inputs (Level 3)
Financial instruments owned:
Contingent purchase consideration assets	1	1
Contingent purchase consideration liabilities
Liabilities:
Contingent purchase consideration liabilities	242	252
Contingent purchase consideration liabilities | Identical Assets (Level 1)
Liabilities:
Contingent purchase consideration liabilities	0	0
Contingent purchase consideration liabilities | Observable Inputs (Level 2)
Liabilities:
Contingent purchase consideration liabilities	0	0
Contingent purchase consideration liabilities | Unobservable Inputs (Level 3)
Liabilities:
Contingent purchase consideration liabilities	$ 242	$ 252