Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										$ 1,091		$ 1,184		$ 1,236
Other non-fee revenues										444		670		663
Total other revenues		$ 328	$ 356	$ 464	$ 387	$ 542	$ 486	$ 436	$ 390	1,535	[1]	1,854	[1]	1,899	[1]
Deferred fee income		$ 3				$ 2				3		2
Credit card fees, net [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										38		67		50
Interchange fees										71		101		88
Rewards program costs										41		44		45
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										132		132		135
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										251		264		284
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										268		302		344
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										48		53		56
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										567		619		684
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										347		354		356
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[2]									$ 7		$ 12		$ 11

[1] See Note 24, "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] Included within other income in the consolidated statement of income (loss).