Loans - Outstanding Balance and Carrying Value of Acquired Loans (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	$ 14,184		$ 16,506
Carrying value	12,898		15,074
Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	2,930		3,272
Carrying value	2,052		2,263
Non-Impaired Loans
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Outstanding balance	11,254		13,234
Carrying value	10,846		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	31		$ 31
Provision for credit losses for Acquired Loans	$ 0	$ 9