Fair Value of the Servicing Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Servicing Assets at Fair Value
Fair value at beginning of period	$ 6
Fair value at end of period	6
Fixed Rate Residential Mortgage
Servicing Assets at Fair Value
Fair value at beginning of period	731	664	732	649
Fair value at end of period	731	664	732	649
Adjustable Rate Residential Mortgage
Servicing Assets at Fair Value
Fair value at beginning of period	35	33	35	32
Fair value at end of period	35	33	35	32
Fixed Rate Automobile Loans
Servicing Assets at Fair Value
Fair value at beginning of period	6
Fair value at end of period	$ 6