Segment Reporting - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	9 Months Ended
Sep. 30, 2012 Segment	Sep. 30, 2011 Global Commercial Bank	Sep. 30, 2011 Global Commercial Bank
Segment Reporting Information [Line Items]
Number of reportable segments	3
Certain changes to the items reported, effect on total net interest income		$ 18.6	$ 52.9

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration