Fair Value of the Servicing Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fixed Rate Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	$ 759	$ 823	$ 935	$ 929
Fair value at end of period	759	823	935	929
Adjustable Rate Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	29	33	37	38
Fair value at end of period	29	33	37	38
Fixed Rate Automobile Loans
Servicing Assets at Fair Value [Line Items]
Fair value at beginning of period	1	2	3	4
Fair value at end of period	$ 1	$ 2	$ 3	$ 4