Loans - Credit Risk Profile of Commercial Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 72,198		$ 67,695		$ 66,705
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	53,033		48,494
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,682		9,034		8,529
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,956		14,446		12,391
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,268		21,625		23,339
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,127		3,389		3,005
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	37,752	[1]	33,567	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,159	[1]	6,069	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,845	[1]	7,279	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,140	[1]	18,636	[1]
Commercial Loan [Member] | External Credit Rating, Investment Grade [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,608	[1]	1,583	[1]
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,281		14,927
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,523		2,965
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,111		7,167
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,128		2,989
Commercial Loan [Member] | External Credit Rating, Non Investment Grade [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,519		$ 1,806

[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.