Loans - Summary of TDRs (Detail) - USD ($)		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Anticipatory TDRs		$ 0
Commercial loans removed from TDR classification		0	$ 0
TDR Loans	[1]	698,000,000		$ 720,000,000
Residential mortgage loan TDR carried at lower of amortized cost or fair value less cost to sell		508,000,000		557,000,000
Non Accrual loans included in TDR loan		318,000,000		230,000,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	[2]	101,000,000		104,000,000
Additional commitments to lend to commercial borrowers with modified TDRs		143,000,000		222,000,000
Commercial Loans [Member] | Business and Corporate Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans		32,000,000		36,000,000
Commercial Loans [Member] | Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans		69,000,000		68,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans		597,000,000		616,000,000
Consumer Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	[3]	561,000,000		580,000,000
Consumer Loans [Member] | Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans	[3]	32,000,000		32,000,000
Consumer Loans [Member] | Credit Cards [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR Loans		$ 4,000,000		$ 4,000,000

[1] At March 31, 2020 and December 31, 2019, the carrying value of TDR Loans includes $318 million and $230 million, respectively, of loans which are classified as nonaccrual.

[2] Additional commitments to lend to commercial borrowers whose loans have been modified in TDR Loans totaled $143 million and $222 million at March 31, 2020 and December 31, 2019, respectively.

[3] At March 31, 2020 and December 31, 2019, the carrying value of consumer mortgage TDR Loans includes $508 million and $557 million, respectively, of loans that are recorded at the lower of amortized cost or fair value of the collateral less cost to sell.