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Pension and Other Postretirement Benefits-Net Periodic Benefit Cost (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Postretirement Plans Other Than Pensions [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost $ 0 $ 1
Net periodic benefit cost 0 1
Hsbc North America [Member] | HSBC North America Pension Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 15 18
Expected return on plan assets (21) (21)
Amortization of net actuarial (gain) loss 5 10
Administrative costs 1 1
Net periodic benefit cost $ 0 $ 8