Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										$ 1,184		$ 1,236		$ 1,233
Other non-fee revenues										670		663		769
Total other revenues		$ 542	$ 486	$ 436	$ 390	$ 363	$ 486	$ 537	$ 513	1,854	[1]	1,899	[1]	2,002	[1]
Immaterial adjustment decreased credit facility fees for fee reversals related to 2018										14
Deferred fee income		$ 2				$ 2				2		2
Credit card fees, net [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										67		50		46
Interchange fees										101		88		79
Rewards program costs										44		45		37
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										132		135		156
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										264		284		291
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										302		344		310
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										53		56		68
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										619		684		669
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers										354		356		348
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[2]									$ 12		$ 11		$ 14

[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).