Expenses - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended	39 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 77,000,000
Charles River Development
Restructuring Cost and Reserve [Line Items]
Acquisitions costs	$ 10,000,000		$ 23,000,000
Charles River Development | Forecast
Restructuring Cost and Reserve [Line Items]
Acquisitions costs				$ 200,000,000
Compensation and Employee Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges		61,000,000
Occupancy Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 16,000,000