Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the period	$ 2		$ 1	$ 5	$ 3
Interest cost	18		17	51	53
Expected return on plan assets	(22)		(22)	(68)	(64)
Amortization of net actuarial (gain) loss	10		8	29	27
Net periodic benefit cost	8		4	17	19
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1		1	2	2
Amortization of net actuarial (gain) loss	0		0	0	(1)
Net periodic benefit cost	$ 1		$ 1	$ 2	$ 1
Hsbc North America [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 46