Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011
Assets
Cash and due from banks	$ 1,528	[1]		$ 1,528	[1]		$ 1,616	[1]
Interest bearing deposits with banks	18,809	[1]		18,809	[1]		25,454	[1]
Federal funds sold and securities purchased under agreements to resell	13,666	[1]		13,666	[1]		3,109	[1]
Trading assets	35,778	[1]		35,778	[1]		38,800	[1]
Loans	56,064	[1]	49,612	56,064	[1]	49,612	51,867	[1]
Other	7,967	[1]		7,967	[1]		6,369	[1]
Total assets	200,427	[1]	178,623	200,427	[1]	178,623	210,280	[1]
Liabilities
Deposits	123,227	[1]	130,655	123,227	[1]	130,655	139,729	[1]
Trading liabilities	20,220	[1]		20,220	[1]		14,186	[1]
Short-term borrowings	10,731	[1]		10,731	[1]		16,009	[1]
Long-term debt	20,014	[1]		20,014	[1]		16,709	[1]
Other liabilities	7,754	[1]		7,754	[1]		4,223	[1]
Total liabilities	182,174	[1]		182,174	[1]		191,778	[1]
Income/(Expense):
Interest income	805		846	1,643		1,708
Interest expense	(270)		(303)	(521)		(535)
Net interest income	535		543	1,122		1,173
Fees and commissions:
Total affiliate income	46		56	102		102
Residential mortgage banking revenue	2		49	27		14
Support services from HSBC affiliates:
Total support services from HSBC affiliates	370		364	738		680
Stock based compensation expense with HSBC	8		15	20		24
HSBC Finance [Member]
Fees and commissions:
Total affiliate income	1		2	2		4
Support services from HSBC affiliates:
Total support services from HSBC affiliates	7		10	17		19
HSBC Markets [Member]
Fees and commissions:
Total affiliate income	5		8	10		11
Support services from HSBC affiliates:
Total support services from HSBC affiliates	74		74	146		122
Other HSBC Affiliates [Member]
Fees and commissions:
Total affiliate income	14		20	42		39
Support services from HSBC affiliates:
Total support services from HSBC affiliates	49		40	101		93
Other HSBC Affiliates Income [Member]
Fees and commissions:
Total affiliate income	26		26	48		48
HSBC Technology and Services [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	240		240	474		446
Parent and Other Subsidiaries of Common Parent [Member]
Assets
Cash and due from banks	212			212			263
Interest bearing deposits with banks	1,141			1,141			1,416
Federal funds sold and securities purchased under agreements to resell	189			189			228
Trading assets	22,605			22,605			22,367
Loans	2,057			2,057			858
Other	907			907			248
Total assets	27,111			27,111			25,380
Liabilities
Deposits	14,959			14,959			18,153
Trading liabilities	25,071			25,071			25,298
Short-term borrowings	3,142			3,142			2,916
Long-term debt	3,989			3,989			3,988
Other liabilities	589			589			451
Total liabilities	47,750			47,750			50,806
Income/(Expense):
Interest income	14		17	27		30
Interest expense	(23)		(21)	(47)		(34)
Net interest income	(9)		(4)	(20)		(4)
Fees and commissions:
Residential mortgage banking revenue	$ 1		$ 2	$ 3		$ 4

[1] The following table summarizes assets and liabilities related to variable interest entities ("VIEs") as of June 30, 2012 and December 31, 2011 which are consolidated on our balance sheet. Assets and liabilities exclude intercompany balances that eliminate in consolidation.