Related Party Transactions - Summary of Related Party Transactions (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Income/(Expense):
Interest income	$ 740		$ 838
Interest expense	(235)		(251)
Net interest income	505	[1]	587	[1]
Servicing and other fees with HSBC affiliates:
Total affiliate income	54		56
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(324)		(368)
Parent And Other Subsidiaries Of Common Parent [Member]
Income/(Expense):
Interest income	22		13
Interest expense	(20)		(24)
Net interest income	2		(11)
Servicing and other fees with HSBC affiliates:
Residential mortgage banking revenue	0		2
Support services from HSBC affiliates:
Stock based compensation expense with HSBC	(9)		(12)
Hsbc Finance And Other Hsbc Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	54		56
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(324)		(368)
HSBC Finance [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	21		14
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(4)		(10)
HSBC Markets [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	5		5
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(52)		(73)
Other HSBC Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	16		28
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(35)		(51)
Other HSBC Affiliates Income [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	12		9
HSBC Technology and Services [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	$ (233)		$ (234)

[1] Net interest income of each segment represents the difference between actual interest earned on assets and interest paid on liabilities of the segment adjusted for a funding charge or credit. Segments are charged a cost to fund assets (e.g. customer loans) and receive a funding credit for funds provided (e.g. customer deposits) based on equivalent market rates. The objective of these charges/credits is to transfer interest rate risk from the segments to one centralized unit in Treasury and more appropriately reflect the profitability of segmen