Bank Premises & Equipment (Bank Premises and Equipment - Additional Information) (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Bank Premises and Equipment
Bank premises impairment	$ 33	$ 2	$ 41	$ 5
Disposal group classified as held for sale | Branch Banking | Bank Premises And Equipment | 2018 Branch Optimization
Bank Premises and Equipment
Parcels Of Undeveloped Land Held for Sale	21		21
Branches and undeveloped parcels of land | Disposal group classified as held for sale | Branch Banking | Bank Premises And Equipment | 2018 Branch Optimization
Bank Premises and Equipment
Parcels Of Undeveloped Land Held for Sale	29		29
Branches and undeveloped parcels of land | Potential branch closures to be selected | Branch Banking | Bank Premises And Equipment | 2018 Branch Optimization
Bank Premises and Equipment
Operating Branch Locations held for sale	128		128