Fee Income from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		$ 323	$ 300	$ 634		$ 629
Other non-fee revenues		214	258	416		522
Total other revenues	[1]	537	558	1,050	[2]	1,151	[2]
Deferred fee income		2		2				$ 1
Credit card fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		15	14	26		25
Interchange fees		22	20	43		39
Rewards program costs		9	7	21		16
Trust and investment management fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		34	39	72		77
Account services [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		73	69	138		137
Credit facilities [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		86	71	164		143
Custodial fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		3	6	5		11
Other fees [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		22	17	37		34
Other fees and commissions [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		184	163	344		325
Servicing and other fees from HSBC affiliates [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers		87	81	186		195
Insurance [Member]
Disaggregation of Revenue [Line Items]
Fee income from contracts with customers	[3]	$ 3	$ 3	$ 6		$ 7

[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 in the consolidated statement of income.