Loans - Status of Commercial Loan Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Financing Receivable, Recorded Investment [Line Items]
Nonaccrual Loans	$ 1,072	$ 1,305
Accruing Loans Contractually Past Due 90 days or More	25	34
Total loans	73,439	67,695	67,710
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	53,966	48,234
Nonaccrual Loans	92	254
Accruing Loans Contractually Past Due 90 days or More	4	6
Total loans	54,062	48,494
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	9,596	8,868
Nonaccrual Loans	65	166
Accruing Loans Contractually Past Due 90 days or More	0	0
Total loans	9,661	9,034	8,919
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	17,327	14,420
Nonaccrual Loans	25	21
Accruing Loans Contractually Past Due 90 days or More	3	5
Total loans	17,355	14,446	13,668
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	24,001	21,560
Nonaccrual Loans	0	65
Accruing Loans Contractually Past Due 90 days or More	0	0
Total loans	24,001	21,625	23,370
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	3,042	3,386
Nonaccrual Loans	2	2
Accruing Loans Contractually Past Due 90 days or More	1	1
Total loans	$ 3,045	$ 3,389	$ 2,552