Pensions and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2014	Sep. 30, 2014 HSBC North America Pension Plan [Member]	Sep. 30, 2013 HSBC North America Pension Plan [Member]	Sep. 30, 2014 HSBC North America Pension Plan [Member]	Sep. 30, 2013 HSBC North America Pension Plan [Member]	Sep. 30, 2014 Postretirement Plans Other Than Pensions [Member]	Sep. 30, 2013 Postretirement Plans Other Than Pensions [Member]	Sep. 30, 2014 Postretirement Plans Other Than Pensions [Member]	Sep. 30, 2013 Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the period		$ 1	$ 1	$ 3	$ 3
Interest cost		17	18	53	52	1	1	2	2
Expected return on assets		(22)	(19)	(64)	(60)
Amortization of (gains) losses		8	10	27	36	0	0	(1)	0
Net periodic benefit cost		4	10	19	31	1	1	1	2
Additional contribution	$ 74