Expenses - Narrative (Details) - USD ($) $ in Millions	12 Months Ended			39 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Repositioning charges	$ 110	$ 300
Charles River Development
Restructuring Cost and Reserve [Line Items]
Acquisitions costs	79	31
Charles River Development | Forecast
Restructuring Cost and Reserve [Line Items]
Acquisitions costs				$ 200
GEAM Business
Restructuring Cost and Reserve [Line Items]
Acquisitions costs			$ 21
Compensation and Employee Benefits
Restructuring Cost and Reserve [Line Items]
Repositioning charges	98	259
Occupancy Costs
Restructuring Cost and Reserve [Line Items]
Repositioning charges	$ 12	$ 41