Acquisitions and Dispositions (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Apr. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2023 USD ($) acquisition	Jun. 30, 2022 USD ($)	Dec. 31, 2022 acquisition	Nov. 01, 2022	Oct. 31, 2022
Business Acquisition [Line Items]
Total consideration						$ 340	$ 158
Cash paid						332	147
Estimated fair value of deferred/contingent consideration						8	11
Deferred purchase consideration from prior years' acquisitions						51	76
Contingent consideration from prior year's acquisitions						134	16
Cash and cash equivalents held in fiduciary capacity			$ 20			(17)	135
Deconsolidation of Russian businesses					$ (39)	0	(39)
Purchase of non-controlling interests						139	0
Beassur SARL
Business Acquisition [Line Items]
Percentage of ownership in equity investment									70.00%	35.00%
U.S. Affinity Business
Business Acquisition [Line Items]
Cash proceeds from sale	$ 140
Gain on disposal	$ 112
Certain Businesses Primarily in Brazil
Business Acquisition [Line Items]
Cash proceeds from sale							3
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions							76
Contingent consideration from prior year's acquisitions						175	34
Pro forma revenue				$ 6			6
Operating income (loss) related to acquisitions				$ 1			$ 1
Advance Asset Management
Business Acquisition [Line Items]
Acquisition related costs		$ 10				27
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration						340
Cash paid						332
Estimated fair value of deferred/contingent consideration						8
Pro forma revenue		41				41
Operating income (loss) related to acquisitions		$ 9				9
Small Individual Financial Advisory Business | Operating Segments
Business Acquisition [Line Items]
Pre-tax loss on sale						$ 17
Risk and Insurance Services
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition						3		16
Consulting
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition						3		4
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)						2 years	2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)						4 years	4 years