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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value Disclosures [Abstract]      
Fair value measurement transfers from one level to another $ 0 $ 0  
Significant changes to the valuation techniques to measure fair value during the reporting period No significant changes to the valuation techniques used by the Company to measure fair value.    
Mortgage loans held for sale measured at fair value gain (loss) $ 27,000,000 185,000,000 $ (335,000,000)
Minimum [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 0.00%    
Maximum [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 98.00%    
Average [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 5.00%    
Standby Letters Of Credit, Unfunded Commitments and Deferred Non-Yield Loan Fees [Member]      
Fair Value Disclosures [Abstract]      
Carrying value of guarantee obligations $ 515,000,000 413,000,000  
Other Guarantees [Member]      
Fair Value Disclosures [Abstract]      
Carrying value of guarantee obligations $ 184,000,000 $ 211,000,000