Loans and Allowance for Credit Losses - Summary of Impaired Loans, which Include Nonaccrual and TDR Loans, by Portfolio Class (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Loan and Lease Receivables, Impaired [Abstract]
Interest income recognized on impaired loans	$ 204
Interest income that would have been recognized on impaired loans at original contractual loan terms	$ 265

The gross interest income that would have been recorded in the period on troubled debt restructurings, if the loans had been current in accordance with their original terms and had been outstanding throughout the period or since origination, if held for part of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18794-111554

Name:	us-gaap_LoansAndLeasesReceivableImpairedTroubledDebtInterestIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration