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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Fair Value Disclosures [Abstract]      
Fair value measurement transfers from one level to another $ 0 $ 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, net gain $ 33,000,000 27,000,000 $ 185,000,000
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 96.00%    
Average [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 3.00%    
Standby Letters Of Credit, Unfunded Commitments and Deferred Non-Yield Loan Fees [Member]      
Fair Value Disclosures [Abstract]      
Carrying value of guarantee obligations $ 618,000,000 515,000,000  
Other Guarantees [Member]      
Fair Value Disclosures [Abstract]      
Carrying value of guarantee obligations $ 186,000,000 $ 184,000,000