Segment Reporting - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012 Segment	Dec. 31, 2011 Global Commercial Bank	Dec. 31, 2010 Global Commercial Bank
Segment Reporting Information [Line Items]
Number of reportable segments	3
Segment reporting change in measurement methods amount		$ 73.7	$ 56.3

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