Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Acquisition [Line Items]
Merger and integration expense	$ 70	$ 6
Personal expense
Business Acquisition [Line Items]
Merger and integration expense	21	1
Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	3	2
Net occupancy expense
Business Acquisition [Line Items]
Merger and integration expense	3	0
Other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 43	$ 3