Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Long-term debt	$ 37,376,000,000			$ 37,376,000,000		$ 37,739,000,000
Derivative, notional amount	4,548,237,000,000			4,548,237,000,000		4,135,130,000,000
Preferred stock issued	1,265,000,000			1,265,000,000		1,265,000,000
Hnah [Member]
Related Party Transaction [Line Items]
Long-term debt	4,900,000,000			4,900,000,000		4,900,000,000
Maximum borrowing capacity	150,000,000			150,000,000		150,000,000
Amount outstanding under the loan agreement	0			0		0
Preferred stock issued						1,265,000,000
Preferred stock outstanding	1,265,000,000			1,265,000,000		1,265,000,000
HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	0			0		2,501,000,000
HSBC Finance Corporation [Member] | Extended Uncommitted Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	5,000,000,000.0			$ 5,000,000,000.0		5,000,000,000.0
Debt term				364 days
Maximum maturity for borrowings under uncommitted revolving credit agreement				5 years
Amount prepaid on credit agreement		$ 2,500,000,000
Credit agreement, prepayment fee paid		$ 28,000,000
HMUS [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	1,742,000,000			$ 1,742,000,000		563,000,000
Extended loans and lines of credit	5,900,000,000			5,900,000,000		5,900,000,000
Amount outstanding on line of credit	1,700,000,000			1,700,000,000		600,000,000
HSBC Mexico [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	0			0		195,000,000
Extended loans and lines of credit	1,200,000,000			1,200,000,000		1,200,000,000
Other HSBC affiliates [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	78,000,000			78,000,000		15,000,000
Extended loans and lines of credit	1,900,000,000			1,900,000,000
Amount outstanding on line of credit	0			0		0
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Long-term debt	4,839,000,000			4,839,000,000		4,834,000,000
Loans and leases receivable from related parties	1,820,000,000			1,820,000,000		3,274,000,000
Derivative, notional amount	761,500,000,000			761,500,000,000		878,500,000,000
Fair value of derivative assets and liabilities	35,000,000			35,000,000		29,000,000
Floating Rate Note Maturing August 2021 [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued	2,000,000,000			2,000,000,000
Floating Rate Note Maturing May 2025 [Member] | Hnah [Member] | Subordinated Debt [Member]
Related Party Transaction [Line Items]
Debt issued	900,000,000			900,000,000
Floating Rate Note Maturing August 2026 [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued	2,000,000,000			2,000,000,000
Support Services From Affiliates [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Rent from related party	$ 13,000,000		$ 16,000,000	$ 41,000,000	$ 47,000,000
Consumer Loans [Member] | Residential Mortgage And Home Equity [Member] | HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Carrying amount of residential mortgage loans						$ 558,000,000