Accumulated Other Comprehensive Loss - (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]				$ 91
Unrealized gains (losses) on investment securities:
Balance at beginning of period		$ (519)	$ (299)	$ (461)
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax		459	(215)	227
Reclassification adjustment for (gains) losses realized in net income (loss), net of tax	[2]	(67)	(18)	(33)
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income (loss), net of tax	[3]	11	13	17
Total other comprehensive income (loss) for period		403	(220)	211
Balance at end of period		(116)	(519)	(299)
Unrealized gains (losses) on fair value option liabilities attributable to our own credit spread:
Balance at beginning of period		301	(23)	174
Other comprehensive income (loss) for period:
Net unrealized gains (losses) arising during period, net of tax		(217)	324	(193)
Reclassification adjustment for a gain realized in net income (loss), net of tax	[4]	(93)	0	0
Total other comprehensive income (loss) for period		(310)	324	(193)
Balance at end of period		(9)	301	(23)
Unrealized gains (losses) on derivatives designated as cash flow hedges:
Balance at beginning of period		(159)
Balance at beginning of period		(159)	(199)	(157)
Other comprehensive income (loss) for period:
Net unrealized gains (losses) arising during period, net of tax		(19)
Reclassification adjustment for losses realized in net income (loss), net of tax	[5]	27
Total other comprehensive income (loss) for period		8
Net unrealized gains (losses) arising during period, net of tax			22	(18)
Reclassification adjustment for gains (losses) realized in net income (loss), net of tax	[5]		18	11
Total other comprehensive income (loss) for period			40	(7)
Balance at end of period			(159)	(199)
Balance at end of period		(151)	(159)
Pension and postretirement benefit liability:
Balance at beginning of period		11	3	0
Change in unfunded pension and postretirement liability, net of tax		(14)	8	2
Total other comprehensive income (loss) for period		(14)	8	2
Balance at end of period		(3)	11	3
Total accumulated other comprehensive loss at end of period		$ (279)	(366)	(431)
Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]		0	4		$ 0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[7]		0	(53)		0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption			0	(4)		0
Accounting Standards Update 2018-02 [Member] | Unrealized Gains (Losses) on Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[7]		0	(35)		0
Accounting Standards Update 2018-02 [Member] | Pension and Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[6]		0	1		0
Accounting Standards Update 2016-01, Fair Value Option [Member] | Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of new accounting principle in period of adoption	[8]		0	0		$ 174
As Previously Reported [Member]
Unrealized gains (losses) on investment securities:
Balance at beginning of period			(250)	(461)
Other comprehensive income for period:
Balance at end of period				(250)
Unrealized gains (losses) on fair value option liabilities attributable to our own credit spread:
Balance at beginning of period			(19)	0
Other comprehensive income (loss) for period:
Balance at end of period				(19)
Unrealized gains (losses) on derivatives designated as cash flow hedges:
Balance at beginning of period			(164)	(157)
Other comprehensive income (loss) for period:
Balance at end of period				(164)
Pension and postretirement benefit liability:
Balance at beginning of period			$ 2	0
Balance at end of period				$ 2

[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

[2] Amount reclassified to net income (loss) is included in other securities gains, net in our consolidated statement of income (loss).

[3] Amount amortized to net income (loss) is included in interest income in our consolidated statement of income (loss). During 2014, we transferred securities from available-for-sale to held-to-maturity. At the date of transfer, AOCI included net pretax unrealized losses related to the transferred securities which are being amortized over the remaining contractual life of each security as an adjustment of yield in a manner consistent with the amortization of any premium or discount.

[4] During the fourth quarter of 2019, HSBC Bank USA repurchased long-term debt that was designated under fair value option. As a result, the cumulative gain attributable to our own credit spread associated with the debt was reclassified to other income in our consolidated statement of income (loss).

[5] Amount reclassified to net income (loss) is included in net interest income in our consolidated statement of income (loss).

[6] As a result of adopting new accounting guidance in 2018, beginning January 1, 2018, changes in fair value for equity securities are recognized in net income (loss). Prior to January 1, 2018, changes in fair value for equity securities classified as available-for-sale were recognized in other comprehensive income.

[7] See Note 17, "Income Taxes," for additional discussion.

[8] As a result of adopting new accounting guidance in 2017, beginning January 1, 2017, the fair value movement on fair value option liabilities attributable to our own credit spread is recorded in other comprehensive income.