Related Party Transactions - Summary of Loans (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	$ 0	$ 2,501
HMUS [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	1,742	563
Extended loans and lines of credit	5,900	5,900
HSBC Mexico [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	0	195
Extended loans and lines of credit	1,200	1,200
Other short-term affiliate lending [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	78	15
Extended loans and lines of credit	1,900
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	$ 1,820	$ 3,274