Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Transfers And Servicing Of Financial Assets [Abstract]
Balance at beginning of period	$ 2,680	$ 1,700
Rights purchased	1	2
Rights capitalized	84	254
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(76)	127
Due to revised assumptions or models	12	(6)
Other changes in fair value	(83)	(122)
Balance at end of period	$ 2,618	$ 1,955