Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2	$ 2	$ 2
Amortization of net actuarial (gain) loss	(2)	(2)	(1)
Net periodic benefit cost	0	0	1
HSBC North America [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	56	60	71
Expected return on plan assets	(78)	(78)	(88)
Amortization of net actuarial (gain) loss	21	31	33
Administrative costs	4	6	4
Loss on partial settlement of Plan pension obligation	0	0	35
Net periodic benefit cost	$ 3	$ 19	$ 55