Bank Premises and Equipment - Summary of Bank Premises and Equipment (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization		$ (3,072)	$ (2,889)
Total bank premises and equipment	[1]	2,088	1,995
Land and and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross		636	639
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 1,612	1,575
Buildings | Lower limit
Property, Plant and Equipment [Line Items]
Useful life		1 year
Buildings | Upper Limit
Property, Plant and Equipment [Line Items]
Useful life		30 years
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 2,302	2,126
Equipment | Lower limit
Property, Plant and Equipment [Line Items]
Useful life		2 years
Equipment | Upper Limit
Property, Plant and Equipment [Line Items]
Useful life		20 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 467	432
Leasehold improvements | Lower limit
Property, Plant and Equipment [Line Items]
Useful life		1 year
Leasehold improvements | Upper Limit
Property, Plant and Equipment [Line Items]
Useful life		30 years
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 108	85
Land and improvements held for sale
Property, Plant and Equipment [Line Items]
Property and equipment, gross		27	8
Buildings held for sale
Property, Plant and Equipment [Line Items]
Property and equipment, gross		8	18
Equipment held for sale
Property, Plant and Equipment [Line Items]
Property and equipment, gross		0	1
Other property
Property, Plant and Equipment [Line Items]
Land improvements		$ 46	$ 51

[1] Includes $35 and $27 of bank premises and equipment held for sale at December 31, 2020 and 2019, respectively. For further information, refer to Note 8.