Loans - Outstanding Balance and Carrying Value of Acquired Loans (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	$ 21,328		$ 25,201
Carrying value(1)	19,753		23,519
Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	3,879		4,279
Carrying value(1)	2,645		2,882
Non-Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	17,449		20,922
Carrying value(1)	17,108		20,637
Receivables Acquired with Deteriorated Credit Quality [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Financing Receivable, Allowance for Credit Losses	28		$ 27
Provision for credit losses for Acquired Loans	$ 1	$ (15)