Fair Value of the Servicing Rights (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Servicing Rights at Fair Value
Fair value at beginning of period	$ 6
Fair value at end of period	6
Fixed Rate Residential Mortgage
Servicing Rights at Fair Value
Fair value at beginning of period		823	929	664
Fair value at end of period		823	929	664
Adjustable Rate Residential Mortgage
Servicing Rights at Fair Value
Fair value at beginning of period		33	38	33
Fair value at end of period		33	38	33
Fixed Rate Automobile Loans
Servicing Rights at Fair Value
Fair value at beginning of period		2	4
Fair value at end of period		$ 2	$ 4