Deposits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total deposits	$ 110,955	[1]	$ 118,702	$ 129,248
Deposits held for sale	10		673
Time Deposits, $250,000 or More [Abstract]
Time Deposits, $250,000 or More	13,076		14,504
Time Deposits, Fiscal Year Maturity [Abstract]
Overdraft deposits	453		321
Domestic Deposits [Member]
Time Deposits, $250,000 or More [Abstract]
Time Deposits, $250,000 or More	12,560		13,875
Time Deposits, Fiscal Year Maturity [Abstract]
0-90 days	8,657
91-180 days	3,253
181-365 days	1,489
2019	13,399
2020	1,130
2021	1,280
2022	1,108
2023	949
Thereafter	3,792
Time deposits	21,658
Foreign Deposits [Member]
Time Deposits, $250,000 or More [Abstract]
Time Deposits, $250,000 or More	516		629
Time Deposits, Fiscal Year Maturity [Abstract]
0-90 days	408
91-180 days	123
181-365 days	1
2019	532
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Time deposits	532
Deposits [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Deposits at fair value	8,154		7,693
Time Deposits, Fiscal Year Maturity [Abstract]
0-90 days	9,065
91-180 days	3,376
181-365 days	1,490
2019	13,931
2020	1,130
2021	1,280
2022	1,108
2023	949
Thereafter	3,792
Time deposits	22,190
Other Expense [Member]
Time Deposits, Fiscal Year Maturity [Abstract]
FDIC assessment fees	135		$ 138	$ 168
Out of Period Adjustments [Member]
Time Deposits, Fiscal Year Maturity [Abstract]
FDIC assessment fees	$ 25

[1] In addition to the changes discussed above, in conjunction with HSBC's adoption of the requirements of IFRS 9 HUSI 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 decreased $0.1 billion and increased $8.3 billion, respectively, and total loans, net and total deposits in the CC segment decreased $2.2 billion and increased $0.3 billion, respectively, at December 31, 2018.