Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Transfers And Servicing Of Financial Assets [Abstract]
Balance at beginning of period	$ 1,955	$ 1,737	$ 1,700	$ 1,519
Rights purchased	3	16	5	29
Rights capitalized	233	215	487	476
Changes in fair value of MSRs
Due to fluctuations in market interest rates	305	(239)	432	(175)
Due to revised assumptions or models	(3)	(18)	(9)	(17)
Other changes in fair value	(116)	(117)	(238)	(238)
Balance at end of period	$ 2,377	$ 1,594	$ 2,377	$ 1,594