Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 23		$ 89
Global Information Technology, HR Functions and Future Rent
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 12		23
Jardine Lloyd Thompson Group plc
Restructuring Cost and Reserve [Line Items]
Costs incurred			42		$ 251
Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, cost incurred to date	628		628
Costs incurred	19	$ 57	42	$ 137
Jardine Lloyd Thompson Group plc | Acquisition related | Corporate
Restructuring Cost and Reserve [Line Items]
Costs incurred	2		3
Jardine Lloyd Thompson Group plc | Acquisition related | Risk and Insurance Services Segment
Restructuring Cost and Reserve [Line Items]
Costs incurred	11		27
Jardine Lloyd Thompson Group plc | Acquisition related | Consulting Segment
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 6		$ 12