Loans - Summary of Criticized Assets for Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 2,018	$ 2,038
Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	698	727
Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	969	715
Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	274	484
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	77	112
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	1,406	1,354
Special Mention [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	392	351
Special Mention [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	749	557
Special Mention [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	198	367
Special Mention [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	67	79
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	602	647
Substandard [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	299	346
Substandard [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	217	156
Substandard [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	76	112
Substandard [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	10	33
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	10	37
Doubtful [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	7	30
Doubtful [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	3	2
Doubtful [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	0	5
Doubtful [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 0	$ 0