Acquisitions and Dispositions (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2023 USD ($) acquisition	Mar. 31, 2022 USD ($)	Dec. 31, 2022 acquisition	Mar. 30, 2023 USD ($)	Nov. 01, 2022	Oct. 31, 2022
Business Acquisition [Line Items]
Total consideration	$ 15	$ 28
Cash paid	11	24
Estimated fair value of deferred/contingent consideration	4	4
Deferred purchase consideration from prior years' acquisitions	12	12
Contingent consideration from prior year's acquisitions	1	4
Transaction costs				$ 252
Deconsolidation of Russian businesses	0	(39)
Beassur SARL
Business Acquisition [Line Items]
Percentage of ownership in equity investment					70.00%	35.00%
Certain Businesses Primarily in Brazil
Business Acquisition [Line Items]
Disposal group, consideration		4
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions		12
Contingent consideration from prior year's acquisitions	1	4
Advance Asset Management
Business Acquisition [Line Items]
Acquisition related costs	17
Small Individual Financial Advisory Business | Operating Segments
Business Acquisition [Line Items]
Pre-tax loss on sale	$ 19
Risk and Insurance Services
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition			16
Risk and Insurance Services | Operating Segments
Business Acquisition [Line Items]
Deconsolidation of Russian businesses		(27)
Consulting
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition	1		4
Consulting | Operating Segments
Business Acquisition [Line Items]
Deconsolidation of Russian businesses		$ (12)
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