Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		$ 298	$ 320	$ 873		$ 954
Other non-fee revenues		188	166	439		582
Total other revenues	[1]	486	486	1,312	[2]	1,536	[2]
Deferred fee income		2		2				$ 2
Credit card fees, net [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		18	12	48		38
Interchange fees		25	22	73		65
Rewards program costs		11	11	33		32
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		34	31	95		103
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		68	70	201	[3]	218	[3]
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		73	90	223		254
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		14	11	40	[3]	43	[3]
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		155	171	464		515
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		88	103	257		289
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[4]	$ 3	3	$ 9		9
Reclassified Amount [Member] | Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers			$ 2			$ 12

[1] See Note 15, "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.

[2] Represents adjustments associated with differences between U.S. GAAP and the Group Reporting Basis.

[3] During the fourth quarter of 2018, we concluded that certain wire transfer fees would be better presented in account services as opposed to other fees. As a result, we have reclassified $2 million and $12 million of wire transfer fees from other fees to account services during the three and nine months ended September 30, 2018 to conform with the current year presentation.

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