Strategic Initiatives - Restructuring Liability (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Restructuring Reserve [Roll Forward]
Restructuring liability at beginning of period		$ 52		$ 45	$ 33		$ 0
Restructuring costs accrued during the period		8		17	49		63
Restructuring costs paid during the period		(7)		(15)	(29)		(16)
Restructuring liability at end of period		53		47	53		47
Severance and Other Employee Costs [Member]
Restructuring Reserve [Roll Forward]
Restructuring liability at beginning of period		6	[1]	22	10	[1]	0
Restructuring costs accrued during the period		3	[1]	13	8	[1]	35
Restructuring costs paid during the period		(2)	[1]	(12)	(11)	[1]	(12)
Restructuring liability at end of period		7	[1]	23	7	[1]	23
Lease Termination and Associated Costs [Member]
Restructuring Reserve [Roll Forward]
Restructuring liability at beginning of period		46	[2]	23	23	[2]	0
Restructuring costs accrued during the period		2	[2]	4	32	[2]	28
Restructuring costs paid during the period		(2)	[2]	(3)	(9)	[2]	(4)
Restructuring liability at end of period		46	[2]	24	46	[2]	24
Other [Member]
Restructuring Reserve [Roll Forward]
Restructuring liability at beginning of period		0		0	0	[3]	0	[3]
Restructuring costs accrued during the period		3		0	9	[3]	0	[3]
Restructuring costs paid during the period		(3)		0	(9)	[3]	0	[3]
Restructuring liability at end of period	[3]	$ 0		$ 0	$ 0		$ 0

[1] Severance and other employee costs are included in salaries and employee benefits in the consolidated statement of income (loss). The majority of these costs were reported in the Wealth and Personal Banking and the Global Banking and Markets business segments. Not included in these costs are allocated severance costs from HSBC Technology & Services ("HTSU") discussed further below.

[2] Primarily includes real estate taxes, service charges and decommissioning costs. Lease termination and associated costs are included in occupancy expense, net in the consolidated statement of income (loss) and were reported in the Wealth and Personal Banking and the Corporate Center business segments.(3)Primarily includes professional fees and other staff costs, which are included in other expenses in the consolidated statement of income (loss).

[3] Primarily includes professional fees and other staff costs, which are included in other expenses in the consolidated statement of income (loss).