Expenses - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended	39 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 0	$ 77,000,000
Charles River Development
Restructuring Cost and Reserve [Line Items]
Acquisitions costs	$ 27,000,000			$ 50,000,000
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