Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 0	$ 0	$ 1	$ 1
Net periodic benefit cost	0	0	1	1
Hsbc North America [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	18	17	36	35
Expected return on plan assets	(22)	(22)	(43)	(42)
Amortization of net actuarial (gain) loss	8	9	18	19
Administrative costs	1	2	2	3
Net periodic benefit cost	$ 5	$ 6	$ 13	$ 15