Loans - Summary of Criticized Assets for Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 2,170	$ 2,158
Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	885	1,409
Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	721	494
Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	502	143
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	62	112
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	1,295	1,125
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	358	627
Special Mention [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	529	369
Special Mention [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	396	93
Special Mention [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	12	36
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	823	916
Substandard [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	511	677
Substandard [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	161	115
Substandard [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	101	50
Substandard [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	50	74
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	52	117
Doubtful [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	16	105
Doubtful [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	31	10
Doubtful [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	5	0
Doubtful [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 0	$ 2