Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		$ 320	$ 299	$ 954		$ 928
Other non-fee revenues		166	94	582		616
Total other revenues	[1]	486	393	1,536	[2]	1,544	[2]
Deferred fee income		2		2				$ 1
Credit card fees, net [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		12	12	38		37
Interchange fees		22	20	65		59
Rewards program costs		11	10	32		26
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		31	39	103		116
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		68	68	206		205
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		90	81	254		224
Custodial fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		3	5	8		16
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		10	13	47		47
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		171	167	515		492
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		103	77	289		272
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[3]	$ 3	$ 4	$ 9		$ 11

[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] Expenses for the segments include fully apportioned corporate overhead expenses.

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