Bank Premises and Equipment - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 256	$ 254	$ 245
Rental income from leased premises	$ 18	17	16
Disposal group classified as held for sale
Property, Plant and Equipment [Line Items]
Operating Branch Locations	107
Parcels Of Undeveloped Land	32
Branch Banking
Property, Plant and Equipment [Line Items]
Bank Premises Impairment	$ 109	20	6
Cancelable And Noncancelable Lease Obligations
Property, Plant and Equipment [Line Items]
Occupancy Costs	$ 110	$ 100	$ 98