Bank Premises & Equipment (Bank Premises and Equipment) (Parenthetical) (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Bank Premises and Equipment
Land and improvements	[1]	$ 636	$ 644
Branches and undeveloped parcels of land
Bank Premises and Equipment
Land and improvements		$ 89	$ 91

[1] (a ) At March 31, 2018 and December 31, 2017 , land and improvements , buildings and construction in progress included $ 89 and $ 9 1 , respectively, associated w ith parcels of undeveloped land intended for future branch ex pansion.