Business Segments Additional Information (Details) $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 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]				$ 91
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 ur own credit spread				$ (85)
Group Reporting Basis [Member] | Retained Earnings [Member] | IFRS 9 [Member]
Segment Reporting Information [Line Items]
Cumulative effect of new accounting principle in period of adoption				(60)
Group Reporting Basis [Member] | Customer Loan Allowance for ECL [Member] | IFRS 9 [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		$ 3	$ 19	$ 55
HSBC North America [Member] | HSBC North America Pension Plan [Member] | Out of Period Adjustments [Member]
Segment Reporting Information [Line Items]
Pension valuation changes related to prior years			$ 10

[1] Reflects the adoption of new accounting guidance in 2018 which resulted in a cumulative effect adjustment as of January 1, 2018 to reclassify the stranded tax effects resulting from the change in the Federal corporate income tax rate discussed above from accumulated other comprehensive loss to retained earnings