Bank Premises and Equipment (Bank Premises and Equipment (Detail)) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment
Land and improvements	[1]	$ 644	$ 663
Buildings	[1]	1,679	1,672
Equipment		1,876	1,761
Leasehold improvements		399	398
Construction in progress	[1]	93	99
Land and improvements held for sale		17	29
Buildings held for sale		9	9
Equipment held for sale		1	1
Accumulated depreciation and amortization		(2,715)	(2,567)
Total bank premises and equipment	[2]	$ 2,003	$ 2,065
Building | Upper Limit
Property, Plant and Equipment
Useful life		30 years
Building | Lower limit
Property, Plant and Equipment
Useful life		2 years
Equipment | Upper Limit
Property, Plant and Equipment
Useful life		20 years
Equipment | Lower limit
Property, Plant and Equipment
Useful life		2 years
Leasehold Improvements | Upper Limit
Property, Plant and Equipment
Useful life		30 years
Leasehold Improvements | Lower limit
Property, Plant and Equipment
Useful life		1 year

[1] (a) At December 31, 2017 and 2016 , land and improvements, buildings and construction in progress included $ 91 and $ 92 , respectively, associated with parcels of undeveloped land intended for future branch expansion.

[2] Includes $ 27 and $ 39 of bank premises and equipment held for sale at December 31, 2017 and 2016 , respectively. For further information refer to N ote 7 .