Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,250	$ 2,618	$ 2,338	$ 2,680
Rights purchased	9	1	15	2
Rights capitalized	164	71	309	155
Rights sold		(141)		(141)
Changes in fair value of MSRs
Due to fluctuations in market interest rates	172	(82)	41	(158)
Due to revised assumptions or models	2	44	2	56
Other changes in fair value	(116)	(99)	(224)	(182)
Balance at end of period	$ 2,481	$ 2,412	$ 2,481	$ 2,412