Mortgage Servicing Assets - Changes in Carrying Amount of Mortgage Servicing Assets (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Servicing Asset [Abstract]
Balance at beginning of period	$ 318	$ 324	$ 321	$ 323
Servicing retained from loan sales	15	18	22	28
Purchases		10	12	25
Amortization	(10)	(23)	(32)	(47)
Balance at end of period	323	329	323	329
Fair value at end of period	$ 404	$ 423	$ 404	$ 423