Sale of Certain Private Banking Client Relationships (Details) - USD ($) $ in Millions	3 Months Ended		13 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Dec. 31, 2017	Aug. 31, 2017
Risks Inherent in Servicing Assets and Servicing Liabilities [Line Items]
Client deposit		$ 121,840	$ 112,090	[1]	$ 118,702
Client investments transferred			1,500
Client deposits transferred			800
Client deposits held for sale			$ 48		673
Portion of Latin America Portfolio [Member] | PB [Member]
Risks Inherent in Servicing Assets and Servicing Liabilities [Line Items]
Client investments						$ 3,500
Client deposit						$ 1,700
Fee, as percent of assets transferred during first 2 years of agreement (percent)			0.50%
Client deposits held for sale			$ 48		$ 673
Additional deposits conditionally eligible for transfer			$ 48
Other assets [Member]
Risks Inherent in Servicing Assets and Servicing Liabilities [Line Items]
Contingent consideration receivable	$ 12	15
Other Income (Loss) [Member]
Risks Inherent in Servicing Assets and Servicing Liabilities [Line Items]
Pre-tax gain (loss) on sale	$ (3)	$ 8

[1] In addition to the changes discussed above, in conjunction with HSBC's adoption of the requirements of IFRS 9 we also adopted changes in presentation under the Group Reporting Basis related to affiliate loans and deposits as well as cash collateral posted and received. Beginning January 1, 2018, affiliate loans have been reclassified from other assets to loans, affiliate deposits have been reclassified from other liabilities to deposits, cash collateral posted has been reclassified from loans to other assets and cash collateral received has been reclassified from deposits to other liabilities. As a result of these changes, total loans, net and total deposits in the GB&M segment increased $0.2 billion and $8.6 billion, respectively, and total loans, net and total deposits in the CC segment decreased $2.0 billion and $1.5 billion, respectively, at September 30, 2018.