Financial Statements of HSBC USA Inc. (Parent) Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ 133	$ (250)	$ 121	$ 109	$ 112	$ 177	$ 269	$ (238)	$ 113	$ 320	$ (179)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization									43	44	51
Net change in other assets and liabilities									1,846	(1,830)	(462)
Net cash provided by (used in) operating activities									(4,259)	(8,185)	105
Cash flows from investing activities
Other, net									119	50	549
Net cash provided by (used in) investing activities									(8,429)	23,375	5,318
Cash flows from financing activities
Net change in short-term borrowings									(535)	(469)	(449)
Issuance of long-term debt, net of issuance costs									4,686	11,923	5,158
Repayment of long-term debt									(10,705)	(14,704)	(8,948)
Return of capital to parent									(2,400)	0	0
Other increases (decreases) in capital surplus									0	6	(18)
Dividends paid									(77)	(76)	(77)
Net cash used in financing activities									(744)	(10,248)	(14,624)
Net change in cash and due from banks and interest bearing deposits with banks									(13,432)	4,942	(9,201)
Cash and due from banks and interest bearing deposits with banks at beginning of period				17,214				12,272	17,214	12,272	21,473
Cash and due from banks and interest bearing deposits with banks at end of period	3,782				17,214				3,782	17,214	12,272
Cash paid for:
Interest									2,921	2,350	1,816
HSBC USA Inc [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									113	320	(179)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization									5	8	12
Net change in other assets and liabilities									1,463	(1,277)	481
Undistributed loss (gain) of subsidiaries									(205)	(380)	369
Other, net									4	16	5
Net cash provided by (used in) operating activities									1,380	(1,313)	688
Cash flows from investing activities
Sales and maturities of securities									0	0	1
Net change in investments in and receivables due from subsidiaries									3,929	(1,045)	2,843
Net change in receivables from other HSBC affiliates									183	4,211	(2,882)
Other, net									1	10	403
Net cash provided by (used in) investing activities									4,113	3,176	365
Cash flows from financing activities
Net change in payables to other HSBC affiliates									4	(19)	(2)
Net change in short-term borrowings									(56)	1,378	(97)
Issuance of long-term debt, net of issuance costs									2,931	5,571	4,826
Repayment of long-term debt									(5,897)	(8,722)	(5,684)
Return of capital to parent									(2,400)	0	0
Other increases (decreases) in capital surplus									0	6	(18)
Dividends paid									(77)	(76)	(77)
Net cash used in financing activities									(5,495)	(1,862)	(1,052)
Net change in cash and due from banks and interest bearing deposits with banks									(2)	1	1
Cash and due from banks and interest bearing deposits with banks at beginning of period				$ 2				$ 1	2	1	0
Cash and due from banks and interest bearing deposits with banks at end of period	$ 0				$ 2				0	2	1
Cash paid for:
Interest									$ 662	$ 649	$ 584