Guarantee Arrangements and Pledged Assets and Collateral - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended						36 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Dec. 31, 2007 HSBC Securities [Member]	Sep. 30, 2013 Available-for-sale Securities [Member]	Dec. 31, 2012 Available-for-sale Securities [Member]	Sep. 30, 2013 Trading Assets [Member]	Dec. 31, 2012 Trading Assets [Member]	Sep. 30, 2013 Financial Guarantee [Member] Collateralized Securities [Member]
Guarantor Obligations [Line Items]
Outstanding financial standby letters of credit	$ 5,200,000,000		$ 5,200,000,000			$ 5,600,000,000
Outstanding financial standby performance guarantees	3,100,000,000		3,100,000,000			2,900,000,000
Deferred fee on stand by letters of credit	40,000,000		40,000,000			46,000,000
Allowance for credit losses on unfunded standby letters of credit	19,000,000		19,000,000			19,000,000
Minimum time to resolve case			3 months
Maximum time to resolve case			12 months
Principal amount outstanding on loans sold to government sponsored entities	12,600,000,000		12,600,000,000			15,100,000,000
Principal amount outstanding on loans from our legacy broker channel	8,100,000,000		8,100,000,000			9,600,000,000
Repurchase demands received from our legacy broker channel	55,000,000	98,000,000	175,000,000	330,000,000
Outstanding repurchase demands on loans sourced from our legacy broker channel	55,000,000		55,000,000			65,000,000
Repurchase liability for loans	198,000,000	216,000,000	198,000,000	216,000,000	217,000,000	219,000,000	222,000,000	237,000,000
Range of possible losses in excess of recorded repurchase liability, minimum														0
Range of possible losses in excess of recorded repurchase liability, maximum														160,000,000
Liquidity facilities	2,200,000,000		2,200,000,000			2,200,000,000
Securities available-for-sale										9,300,000,000	6,500,000,000
Fair value of collateral received												3,400,000,000	2,200,000,000
Separately reported available-for-sale pledged assets	4,300,000,000		4,300,000,000			5,700,000,000
Securities sold under agreements to repurchase	2,100,000,000		2,100,000,000			1,300,000,000
Whole loan securitization									$ 24,000,000,000