Bank Premises and Equipment - Summary of Bank Premises and Equipment (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization		$ (3,081)	$ (3,072)
Total bank premises and equipment	[1]	2,072	2,088
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross		2,328	2,302
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, gross		1,596	1,612
Land and and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross		635	636
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross		462	467
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross		105	108
Land and improvements held for sale
Property, Plant and Equipment [Line Items]
Property and equipment, gross		19	27
Buildings held for sale
Property, Plant and Equipment [Line Items]
Property and equipment, gross		8	8
Other property
Property, Plant and Equipment [Line Items]
Land improvements		$ 49	$ 46

[1] Includes $27 and $35 of bank premises and equipment held for sale at March 31, 2021 and December 31, 2020, respectively.