Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										$ 1,236		$ 1,233		$ 1,235
Other non-fee revenues										663		769		169
Total other revenues		$ 363	$ 486	$ 537	$ 513	$ 458	$ 393	$ 558	$ 593	1,899	[1]	2,002	[1]	1,404	[1],[2]
Deferred fee income		$ 2				$ 1				2		1
Credit card fees, net [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										50		46		52
Interchange fees										88		79		76
Rewards program costs										45		37		30
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										135		156		153
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										284		291		293
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										344		310		349
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										56		68		79
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										684		669		721
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										356		348		289
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[3]									$ 11		$ 14		$ 20

[1] Represents adjustments associated with differences between U.S. GAAP and the Group Reporting Basis. These adjustments, which are more fully described above, consist of the following: NetInterestIncome OtherRevenues Provisionfor CreditLosses OperatingExpenses Profit (Loss)before IncomeTax Expense TotalAssets (in millions)December 31, 2018 Deposit incentives$9 $— $— $20 $(11) $(10)Derivatives— — — — — (30,866)Expected credit losses / loan impairment(6) — 118 — (124) (386)Goodwill— — — — — 347Loan origination(29) (3) — (14) (18) 45Loans held for sale9 6 (3) — 18 45Pension and other postretirement benefit costs— — — 8 (8) (44)Property— — — (8) 8 7Securities transferred to held-to-maturity— — — — — (76)Other1 (12) — (3) (8) 11Total adjustments$(16) $(9) $115 $3 $(143) $(30,927) December 31, 2017 Derivatives$— $— $— $— $— $(32,900)Expected credit losses / loan impairment(43) — (72) — 29 (332)Goodwill— (1) — — (1) 347Loan origination(19) — — (14) (5) 42Loans held for sale9 141 — — 150 21Pension and other postretirement benefit costs— — — 94 (94) (263)Property— — — (11) 11 8Structured notes and deposits— 85 — — 85 —Other5 (25) — 6 (26) (1)Total adjustments$(48) $200 $(72) $75 $149 $(33,078) December 31, 2016 Derivatives$— $— $— $— $— $(44,911)Expected credit losses / loan impairment(57) 7 (58) 1 7 (326)Goodwill— — — — — 348Loan origination(21) — — (19) (2) 35Loans held for sale— (80) (20) — (60) (31)Pension and other postretirement benefit costs— — — 19 (19) (191)Property— — — (19) 19 16Unquoted equity securities— — — — — (163)Other2 (31) — (8) (21) (11)Total adjustments$(76) $(104) $(78) $(26) $(76) $(45,234)

[2] See Note 23, "Business Segments," for a reconciliation of total other revenues on a U.S. GAAP basis to other operating income for each business segment under the Group Reporting Basis.

[3] Included within other income (loss) in the consolidated statement of income (loss).