Loans - Credit Risk Profile of Commercial Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 66,705		$ 63,258		$ 56,064
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	47,264		44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,529		8,457		7,977
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,391		12,608		11,256
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,339		20,009		15,042
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,005		3,076		3,142
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,047	[1]	28,198	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,010	[1]	4,727	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,912	[1]	6,012	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,927	[1]	16,206	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,198	[1]	1,253	[1]
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,217		15,952
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,519		3,730
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,479		6,596
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,412		3,803
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,807		$ 1,823

[1] Investment grade includes commercial loans with credit ratings of at least BBB- or above or the equivalent based on our internal credit rating system.