Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Transfers And Servicing Of Financial Assets [Abstract]
Balance at beginning of period	$ 2,377	$ 1,594	$ 1,700	$ 1,519
Rights purchased	2	10	7	39
Rights capitalized	187	224	674	700
Changes in fair value of MSRs
Due to fluctuations in market interest rates	71	(123)	503	(298)
Due to revised assumptions or models	42	(2)	33	(19)
Other changes in fair value	(102)	(150)	(340)	(388)
Balance at end of period	$ 2,577	$ 1,553	$ 2,577	$ 1,553