Business Segments Additional Information (Details) $ in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment		5
Cumulative effect of new accounting principle in period of adoption	[1]		$ 0	$ 0	$ 91
Lessee, Operating Lease, Term of Contract			5 years	10 years
Other Revenues under the Group Reporting Basis [Member]
Segment Reporting Information [Line Items]
Gains (losses) from the fair value movement on structured notes and deposits attributable to our own credit spread			$ (85)	$ (33)
IFRS 9 [Member] | Group Reporting Basis [Member] | Retained Earnings [Member]
Segment Reporting Information [Line Items]
Cumulative effect of new accounting principle in period of adoption			(60)
IFRS 9 [Member] | Group Reporting Basis [Member] | Customer Loan Allowance for ECL [Member]
Segment Reporting Information [Line Items]
Cumulative effect of new accounting principle in period of adoption			60
HSBC North America [Member] | HSBC North America Pension Plan [Member]
Segment Reporting Information [Line Items]
Pension valuation changes related to prior years		$ 8	$ 55	$ 30
Out of Period Adjustments [Member] | HSBC North America [Member] | HSBC North America Pension Plan [Member]
Segment Reporting Information [Line Items]
Pension valuation changes related to prior years		$ 10

[1] See Note 2, "Summary of Significant Accounting Polices and New Accounting Pronouncements," for additional discussion.