Nonperforming Assets (Additional Information) (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Other Real Estate	[1]	$ 57	$ 60
Accrual Loans [Member]
Mortgage Loans in Process of Foreclosure, Amount		101	122
Proceeds due from FHA or VA [Member]
Mortgage Loans in Process of Foreclosure, Amount		97	114
Other Real Estate		45	50
Nonaccrual loans [Member]
Mortgage Loans in Process of Foreclosure, Amount		73	85
Residential Portfolio Segment [Member]
Other Real Estate		51	50
Commercial Portfolio Segment [Member]
Other Real Estate		4	7
Land and Land Improvements [Member]
Other Real Estate		$ 2	$ 3

[1] Does not include foreclosed real estate related to loans insured by the FHA or guaranteed by the VA. Proceeds due from the FHA and the VA are recorded as a receivable in Other assets in the Consolidated Balance Sheets until the property is conveyed and the funds are received. The receivable related to proceeds due from the FHA and the VA totaled $45 million and $50 million at December 31, 2017 and 2016, respectively.