Bank Premises and Equipment (Parenthetical) (Detail) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Land and improvements	[1]	$ 685	$ 793
Branches and undeveloped parcels of land
Property, Plant and Equipment [Line Items]
Land and improvements		$ 102	$ 165

[1] At December 31, 2015 and 2014, land and improvements included $102 and $165, respectively, associated with parcels of undeveloped land intended for future branch expansion.