Related Party Transactions - Summary of Related Party Transactions (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012	Dec. 31, 2011
Assets:
Cash and due from banks	$ 1,512,000,000		$ 1,359,000,000		$ 1,385,000,000	$ 1,616,000,000
Interest bearing deposits with banks	29,917,000,000		13,279,000,000
Trading assets	25,527,000,000		30,874,000,000
Loans	67,710,000,000		63,258,000,000		61,452,000,000
Other	8,585,000,000		7,069,000,000
Total assets	187,375,000,000	[1]	191,446,000,000	[1]	198,583,000,000
Liabilities:
Deposits	112,921,000,000		117,671,000,000		121,335,000,000
Trading liabilities	11,065,000,000		14,699,000,000
Short-term borrowings	19,499,000,000		14,933,000,000
Long-term debt	22,151,000,000		21,745,000,000
Other	4,357,000,000		4,562,000,000
Total liabilities	169,993,000,000	[1]	173,610,000,000	[1]
Parent And Other Subsidiaries Of Common Parent [Member]
Assets:
Cash and due from banks	343,000,000		114,000,000
Interest bearing deposits with banks	1,028,000,000	[2]	714,000,000	[2]
Trading assets	17,169,000,000	[3]	21,370,000,000	[3]
Loans	5,854,000,000		4,514,000,000
Other	765,000,000	[4]	858,000,000	[4]
Total assets	25,159,000,000		27,570,000,000
Liabilities:
Deposits	16,577,000,000		13,863,000,000
Trading liabilities	19,692,000,000	[3]	23,910,000,000	[3]
Short-term borrowings	1,950,000,000		2,721,000,000
Long-term debt	3,990,000,000		3,990,000,000
Other	606,000,000	[3]	459,000,000	[3]
Total liabilities	$ 42,815,000,000		$ 44,943,000,000

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities (“VIEs”) as of September 30, 2013 and December 31, 2012 which are consolidated on our balance sheet. Assets and liabilities exclude intercompany balances that eliminate in consolidation. September 30, December 31, 2013 2012 (in millions)Assets Interest bearing deposits with banks$5 $—Securities held-to-maturity208 —Other assets479 533Total assets$692 $533Liabilities Long-term debt92 92Interest, taxes and other liabilities99 152Total liabilities$191 $244

[2] Includes interest bearing deposits with HSBC Mexico S.A. of $800 million and $500 million at September 30, 2013 and December 31, 2012, respectively.

[3] Trading assets and liabilities do not reflect the impact of netting which allows the offsetting of amounts relating to certain contracts if certain conditions are met. Trading assets and liabilities primarily consist of derivatives contracts.

[4] Other assets and other liabilities primarily consist of derivative contracts.