Loans - Status of Commercial Loan Portfolio (Detail) - USD ($) $ in Millions	Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Accruing Loans Contractually Past Due 90 days or More	$ 23		$ 21
Total loans	72,478		68,978		$ 66,399
Commercial Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Performing Loans	52,594		49,198
Nonaccrual Loans	150		143
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	52,745		49,342
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Performing Loans	11,697		11,337
Nonaccrual Loans	7		7
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	11,704		11,344		11,245
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Performing Loans	14,219		12,995
Nonaccrual Loans	90		70
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	14,310		13,066		12,109
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Performing Loans	20,843		20,102
Nonaccrual Loans	53		65
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	20,896	[1]	20,167	[1]	18,877
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Performing Loans	5,835		4,764
Nonaccrual Loans	0		1
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	$ 5,835	[2]	$ 4,765	[2]	$ 4,612

[1] Represents large multinational firms including globally focused U.S. corporate and financial institutions, U.S. dollar lending to multinational banking clients managed by HSBC on a global basis and complex large business clients supported by Global Banking and Markets relationship managers.

[2] Includes loans to HSBC affiliates which totaled $3,096 million and $2,274 million at June 30, 2019 and December 31, 2018, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.