Bank Premises and Equipment (Parenthetical) (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Bank Premises And Equipment [Line Items]
LandImprovements	[1]	$ 713	$ 793
Branches and undeveloped parcels of land
Bank Premises And Equipment [Line Items]
LandImprovements		$ 102	$ 165

[1] At September 30, 2015 and December 31, 2014, land and improvements included $102 million and $165 million, respectively, associated with parcels of undeveloped land intended for future branch expansion.