Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension expense, out of period adjustment	$ 4	$ 6
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	2	2	$ 2
Amortization of net actuarial (gain) loss	(1)	0	0
Net periodic benefit cost	1	2	2
Hsbc North America [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	71	70	70
Expected return on plan assets	(88)	(86)	(90)
Amortization of net actuarial (gain) loss	33	42	38
Administrative costs	4	4	5
Loss on partial settlement of Plan pension obligation	35	0	0
Net periodic benefit cost	$ 55	$ 30	$ 23