Retained Earnings and Regulatory Capital Requirements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repayments of Long-term Debt			$ 9,387,000,000	$ 2,921,000,000
Contributions			4,000,000,000	0
Payments for repurchase of redeemable preferred stock	$ 300,000,000		300,000,000	$ 0
HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Contributions		$ 4,000,000,000
Common Stock [Member] | HSBC Bank USA, National Association [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Distributions		$ 2,400,000,000
Number of shares of common stock issued to parent		2
Common Stock [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Number of shares of common stock issued to parent		1
Noncumulative Preferred Stock [Member] | HSBC Bank USA, National Association [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Distributions		$ 2,500,000,000
Number of shares of common stock issued to parent		250
Adjustable Rate Cumulative Preferred Stock, Series D [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, redemption price per share (usd per share)	$ 100
$2.8575 Cumulative Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividend per share (usd per share)	2.8575
Preferred stock, redemption price per share (usd per share)	$ 50
Senior debt [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repayments of Long-term Debt		$ 4,000,000,000
Subordinated Debt [Member] | HSBC Bank USA, National Association [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repayments of Long-term Debt		$ 900,000,000
Junior Subordinated Debentures [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Junior subordinated debentures called during the period	$ 560,000,000
Loss on extinguishment of debentures	$ 11,000,000
Junior Subordinated Debentures Issued to HSBC USA Capital Trust I [Member] | Junior Subordinated Debentures [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Contractual call price (percent)	100.781%
Junior Subordinated Debentures Issued to HSBC USA Capital Trust II [Member] | Junior Subordinated Debentures [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Contractual call price (percent)	100.84%
Junior Subordinated Debentures Issued to HSBC USA Capital Trust III [Member] | Junior Subordinated Debentures [Member] | HSBC USA Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Contractual call price (percent)	100.732%
Hnah [Member] | Floating Rate Notes [Member] | Senior debt [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Debt issued			1,000,000,000		$ 4,000,000,000
Hnah [Member] | Floating Rate Notes [Member] | Subordinated Debt [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Debt issued	$ 850,000,000		$ 850,000,000