Financial Statements of HSBC USA Inc. (Parent) Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (773)	$ 94	$ 204	$ 296	$ (37)	$ 33	$ (21)	$ 154	$ (179)	$ 129	$ 330
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									51	60	59
Net change in other assets and liabilities									(454)	1,726	386
Net cash provided by (used in) operating activities									113	(3)	4,651
Cash flows from investing activities
Other, net									546	111	(386)
Net cash provided by (used in) investing activities									14,396	(14,102)	(9,523)
Cash flows from financing activities
Net change in short-term borrowings									(449)	110	(7,806)
Issuance of long-term debt, net of issuance costs									5,158	8,694	16,586
Repayment of long-term debt									(8,953)	(4,869)	(9,937)
Preferred stock issuance									0	1,265	0
Preferred stock redemption									0	(1,265)	(300)
Capital contribution from parent									0	0	4,000
Other increases (decreases) in capital surplus									(18)	(21)	(1)
Dividends paid									(77)	(67)	(65)
Net cash provided by (used in) financing activities									(14,629)	14,372	4,949
Net change in cash and due from banks									(120)	267	77
Cash and due from banks at beginning of period				1,235				968	1,235	968	891
Cash and due from banks at end of period	1,115				1,235				1,115	1,235	968
Cash paid for:
Interest									1,811	1,446	942
HSBC USA Inc [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									(179)	129	330
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									12	14	25
Net change in other assets and liabilities									485	274	517
Undistributed loss (gain) of subsidiaries									369	(7)	(308)
Other, net									5	(4)	(31)
Net cash provided by (used in) operating activities									692	406	533
Cash flows from investing activities
Purchases of securities									0	0	(56)
Sales and maturities of securities									1	254	298
Net change in investments in and receivables due from subsidiaries									2,843	(496)	(4,489)
Net change in receivables from other HSBC affiliates									(2,882)	887	835
Other, net									403	(27)	(38)
Net cash provided by (used in) investing activities									365	618	(3,450)
Cash flows from financing activities
Net change in payables to other HSBC affiliates									(2)	19	0
Net change in short-term borrowings									(97)	(727)	(2,794)
Issuance of long-term debt, net of issuance costs									4,826	3,587	11,946
Repayment of long-term debt									(5,689)	(3,815)	(9,870)
Preferred stock issuance									0	1,265	0
Preferred stock redemption									0	(1,265)	(300)
Capital contribution from parent									0	0	4,000
Other increases (decreases) in capital surplus									(18)	(21)	(1)
Dividends paid									(77)	(67)	(65)
Net cash provided by (used in) financing activities									(1,057)	(1,024)	2,916
Net change in cash and due from banks									0	0	(1)
Cash and due from banks at beginning of period				$ 0				$ 0	0	0	1
Cash and due from banks at end of period	$ 0				$ 0				0	0	0
Cash paid for:
Interest									$ 579	$ 517	$ 406