Loans - Changes in Accretable Yield on Acquired Loans (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield, beginning balance	$ 3,997	$ 4,653
Accretion recognized in earnings	(192)	(637)
Reclassifications from (to) nonaccretable difference for loans with changing cash flows(1)	2	36
Changes in accretable yield for non-credit related changes in expected cash flows(2)	(136)	(381)
Accretable yield, ending balance	3,671	3,671
Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield, beginning balance	1,412	1,485
Accretion recognized in earnings	(65)	(222)
Reclassifications from (to) nonaccretable difference for loans with changing cash flows(1)	1	46
Changes in accretable yield for non-credit related changes in expected cash flows(2)	(22)	17
Accretable yield, ending balance	1,326	1,326
Non-Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield, beginning balance	2,585	3,168
Accretion recognized in earnings	(127)	(415)
Reclassifications from (to) nonaccretable difference for loans with changing cash flows(1)	1	(10)
Changes in accretable yield for non-credit related changes in expected cash flows(2)	(114)	(398)
Accretable yield, ending balance	$ 2,345	$ 2,345