Fair Value of the Servicing Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Fixed Rate Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	$ 823	$ 898	$ 929
Fair value at end of period	731	823	898
Adjustable Rate Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	33	35	38
Fair value at end of period	25	33	35
Fixed Rate Automobile Loans
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	2	2	4
Fair value at end of period	$ 1	$ 2	$ 2