Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other loans included in impaired loans apart from TDR loans	$ 329	$ 571
Residential mortgage loan TDR carried at lower of amortized cost or fair value less cost to sell	655	672	$ 881
Non Accrual loans included in TDR loan	559	645
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional commitments to lend to commercial borrowers with modified TDRs	$ 245	$ 184