Pensions and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 1	$ 1
Amortization of transition obligation	0	1
Net periodic benefit cost	1	2
Parent [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the period	1	3
Interest cost on projected benefit obligation	17	17
Expected return on assets	(20)	(21)
Amortization of prior service cost (benefit)	0	(1)
Recognized losses	13	11
Net periodic benefit cost	$ 11	$ 9