Loans - Impaired Commercial Loans Considered as TDR Loans (Detail) (Commercial Loans [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	$ 421	$ 597
Amount without Impairment Reserves	449	490
Total Impaired Commercial Loans	870	1,087
Impairment Reserve	128	216
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	235	391
Amount without Impairment Reserves	298	342
Total Impaired Commercial Loans	533	733
Impairment Reserve	102	114
Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	58	68
Amount without Impairment Reserves	50	59
Total Impaired Commercial Loans	108	127
Impairment Reserve	10	12
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	3	1
Amount without Impairment Reserves	83	89
Total Impaired Commercial Loans	86	90
Impairment Reserve	1
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Amount with Impairment Reserves	125	137
Amount without Impairment Reserves	18
Total Impaired Commercial Loans	143	137
Impairment Reserve	$ 15	$ 90