Loans - Summary of TDRs (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	$ 200	$ 786
Residential mortgage loan TDR carried at lower of amortized cost or fair value less cost to sell	104	487
Non Accrual loans included in TDR loan	115	463
Commercial loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	63	168
Additional commitments to lend to commercial borrowers with modified TDRs	13	107
Commercial loans: | Cares Act Election
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans excluded from TDR classification	42	924
Commercial loans: | Business and corporate banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	38	94
Commercial loans: | Global banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	25	74
Consumer loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	137	618
Consumer loans: | Loans held for sale | Exit of Mass Market Retail Banking Business and Remaining Retail Credit Card Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	416
Consumer loans: | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	125	582
Consumer loans: | Home equity mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	9	31
Consumer loans: | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	3	5
Consumer loans: | Mortgage Loans Under Covid-19 Payment Deferral | Cares Act Election
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans excluded from TDR classification	$ 16	$ 736