Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended		33 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	$ 70	$ 89
RIS
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	31
Consulting
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	12
Corporate
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	27
JLT Transaction
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	93	251
JLT Transaction | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Incurred integration and restructuring costs			$ 679
Program to date	93	$ 251	$ 93
JLT Transaction | RIS | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	53
JLT Transaction | Consulting | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	36
JLT Transaction | Corporate | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Costs incurred in other restructuring	$ 4