Derivative Instruments and Other Financial Instruments Used For Hedging - Additional Information (Detail) (USD $)	6 Months Ended
Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Income from accumulated other comprehensive income to net interest income	$ 33,000,000
Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Weighted average remaining life of the currently active cash flow hedges	3 years 7 months 24 days
LIBOR indexed loans [Member] \| Interest rate swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount	$ 2,000,000,000

Amount of unrealized gain (loss) related to the increase or decrease in fair value of interest rate derivatives designated as cash flow hedging instruments, which was recorded in accumulated other comprehensive income to the extent that the cash flow hedge was determined to be effective.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 46

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration