Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Business Acquisition [Line Items]
Merger and integration expense	$ 32	$ 14	$ 102	$ 20
Personal expense
Business Acquisition [Line Items]
Merger and integration expense	16	5	37	6
Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	4	5	7	7
Net occupancy expense
Business Acquisition [Line Items]
Merger and integration expense	0	(1)	3	(1)
Other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 12	$ 5	$ 55	$ 8