Securities Available for Sale - Additional Information (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Mortgage-backed Securities, Issued by Private Enterprises [Member]	Dec. 31, 2012 Mortgage-backed Securities, Issued by Private Enterprises [Member]	Jun. 30, 2013 Impaired Securities Mortgage-backed Securities, Issued by Private Enterprises [Member]	Jun. 30, 2012 Impaired Securities Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities Pledged as Collateral	$ 9,300,000,000	$ 10,600,000,000
Securities AFS Pledged Transferee Can Transfer	0	0
Available-for-sale Securities	$ 23,389,000,000	$ 21,953,000,000	$ 181,000,000	$ 209,000,000	$ 2,000,000	$ 140,000,000

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

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-Name Statement of Financial Accounting Standard (FAS)

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-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.

+ Details