Bank Premises and Equipment (Bank Premises and Equipment - Additional Information (Detail)) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Depreciation and amortization expense	$ 234	$ 242	$ 256
Deferred Gain on Transaction	11
Branch Banking
Property, Plant and Equipment
Bank Premises Impairment	7	32	109
Cancelable And Noncancelable Lease Obligations
Property, Plant and Equipment
Occupancy Costs	101	100	110
Rental income from leased premises	$ 13	$ 16	$ 18