Loans - Summary of Criticized Assets for Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 1,763	$ 2,158
Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	972	1,409
Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	529	494
Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	196	143
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	66	112
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	909	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	455	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	372	369
Special Mention [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	72	93
Special Mention [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	10	36
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	818	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	494	677
Substandard [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	147	115
Substandard [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	124	50
Substandard [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	53	74
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	36	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	23	105
Doubtful [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	10	10
Doubtful [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	0	0
Doubtful [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 3	$ 2