Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Impaired [Line Items]
Total	$ 65	$ 59	$ 140	$ 105
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	28	11	67	21
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	4	0	4	0
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	24	11	50	11
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	13	0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	0	10
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	37	48	73	84
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	35	46	70	79
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Total	1	1	1	2
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 1	$ 1	$ 2	$ 3