Loans - Outstanding Balance and Carrying Value of Acquired Loans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	$ 15,443		$ 16,506
Carrying value	14,108		15,074
Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	3,119		3,272
Carrying value	2,180		2,263
Non-Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	12,324		13,234
Carrying value	11,928		12,811
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	32		$ 31
Provision for credit losses for Acquired Loans	$ 1	$ (2)