Net income from financial instruments measured at fair value through profit and loss - Net income/(expense) arising from financial instruments measured at fair value through profit or loss (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of financial assets and liabilities [Line Items]
Net income from financial instruments held for trading or managed on a fair value basis		$ 9,582	$ 10,231	$ 9,531
Net income/(expense) from assets and liabilities of insurance businesses, including related derivatives, measured at fair value through profit or loss		2,081	3,478	(1,488)
Changes in fair value of designated debt and related derivatives	[1]	231	90	(97)
Changes in fair value of other financial instruments mandatorily measured at fair value through profit or loss		455	812	695
Net income/expense from financial instruments measured at fair value through profit and loss		12,349	14,611	8,641
Liabilities to customers under investment contracts
Disclosure of financial assets and liabilities [Line Items]
Net income/(expense) from assets and liabilities of insurance businesses, including related derivatives, measured at fair value through profit or loss		(400)	(352)	97
Derivatives managed in conjunction with HSBC’s issued debt securities
Disclosure of financial assets and liabilities [Line Items]
Changes in fair value of designated debt and related derivatives		2,619	2,561	(626)
Other changes in fair value
Disclosure of financial assets and liabilities [Line Items]
Changes in fair value of designated debt and related derivatives		(2,388)	(2,471)	529
Trading securities
Disclosure of financial assets and liabilities [Line Items]
Net income from financial instruments held for trading or managed on a fair value basis		11,074	16,121	6,982
Other instruments managed on a fair value basis
Disclosure of financial assets and liabilities [Line Items]
Net income from financial instruments held for trading or managed on a fair value basis		(1,492)	(5,890)	2,549
Financial assets held to meet liabilities under insurance and investment contracts
Disclosure of financial assets and liabilities [Line Items]
Net income/(expense) from assets and liabilities of insurance businesses, including related derivatives, measured at fair value through profit or loss		$ 2,481	$ 3,830	$ (1,585)

[1] The debt instruments, issued for funding purposes, are designated under the fair value option to reduce an accounting mismatch.