Related Party Transactions - Summary of Related Party Transactions (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Related Party Transaction [Line Items]
Interest income	$ 757		$ 805		$ 1,497		$ 1,643
Interest expense	(239)		(270)		(474)		(521)
Net interest income	518	[1]	535	[1]	1,023	[1]	1,122	[1]
Servicing and other fees with HSBC affiliates:
Total affiliate income	59		46		113		102
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(362)		(386)		(686)		(771)
Parent And Other Subsidiaries Of Common Parent [Member]
Related Party Transaction [Line Items]
Interest income	83		14		105		27
Interest expense	(19)		(23)		(39)		(47)
Net interest income	64		(9)		66		(20)
Servicing and other fees with HSBC affiliates:
Residential mortgage banking revenue	0		1		0		3
Support services from HSBC affiliates:
Stock based compensation expense with HSBC	(13)		(8)		(22)		(20)
Hsbc Finance And Other Hsbc Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	59		46		113		102
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(362)		(386)		(686)		(771)
HSBC Finance [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	26		17		47		30
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(5)		(7)		(9)		(17)
HSBC Markets [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	4		5		9		10
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(54)		(79)		(106)		(161)
Other HSBC Affiliates [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	14		14		30		42
Support services from HSBC affiliates:
Total support services from HSBC affiliates	(61)		(60)		(96)		(119)
Other HSBC Affiliates Income [Member]
Servicing and other fees with HSBC affiliates:
Total affiliate income	15		10		27		20
HSBC Technology and Services [Member]
Support services from HSBC affiliates:
Total support services from HSBC affiliates	$ (242)		$ (240)		$ (475)		$ (474)

[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 segments.