Loans - Summary of Criticized Assets for Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	$ 1,994	$ 2,158
Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	1,149	1,409
Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	453	494
Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	292	143
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	100	112
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	1,144	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	510	627
Special Mention [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	363	369
Special Mention [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	242	93
Special Mention [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	29	36
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	810	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	611	677
Substandard [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	81	115
Substandard [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	50	50
Substandard [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	68	74
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	40	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	28	105
Doubtful [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases doubtful receivable commercial net of deferred income	9	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