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Mortgage Servicing Assets - Additional Information (Detail) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Aug. 01, 2016
Commercial Mortgage Backed Securities [Member]      
Servicing Assets at Fair Value [Line Items]      
Contractual fee income from servicing commercial mortgage loans $ 101 $ 104  
Amortization of servicing commercial mortgage loans 66 $ 71  
Residential Mortgage Backed Securities [Member]      
Servicing Assets at Fair Value [Line Items]      
Contractual fee income from servicing commercial mortgage loans 3    
Amortization of servicing commercial mortgage loans $ 1    
Residential Mortgage Backed Securities [Member] | First Niagara Bank, N.A. [Member]      
Servicing Assets at Fair Value [Line Items]      
Fair value of mortgage servicing assets     $ 28