Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1	$ 1	$ 2	$ 2
Net periodic benefit cost	1	1	2	2
Hsbc North America [Member] | HSBC North America Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	18	18	53	51
Expected return on plan assets	(21)	(22)	(63)	(68)
Amortization of net actuarial (gain) loss	13	10	32	29
Administrative costs	1	2	4	5
Net periodic benefit cost	11	$ 8	26	$ 17
Out of period adjustment	$ 6		$ 6