Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Estimated remaining costs	$ 219	$ 219
JLT Transaction
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring		427	$ 163
Acquisition Related | JLT Transaction
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring		427	163
Acquisition Related | JLT Transaction | Corporate
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring		96	31
RIS
Restructuring Cost and Reserve [Line Items]
Exit costs	$ 89
RIS | Acquisition Related | JLT Transaction
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring		254	84
Consulting | Acquisition Related | JLT Transaction
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring		$ 77	$ 48