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Goodwill and Other Intangible Assets - Summary of the Key Characteristics, Inputs, and Economic Assumptions Used to Estimate the Fair Value of the Company's MSRs (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Mortgage Servicing Rights, Fair Value [Member]      
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed 13.00% 9.00%  
Decline in fair value from 10% adverse change $ 85 $ 50  
Decline in fair value from 20% adverse change $ 160 $ 97  
Discount rate (annual) 4.00% 8.00%  
Decline in fair value from 10% adverse change $ 47 $ 63  
Decline in fair value from 20% adverse change $ 90 $ 122  
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Weighted Average Life 5 years 5 months 7 years  
Weighted-average coupon 3.90% 4.00%  
Commercial Mortgage Servicing Rights [Member]      
Servicing Asset at Fair Value, Amount $ 75 $ 62  
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate 12.00% 12.00%  
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed 7.00% 6.00%  
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions used to Estimate Fair Value, Float Earnings Rate 1.10% 0.50%  
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Weighted Average Life 7 years 7 years  
Mortgage Servicing Rights, Fair Value [Member]      
Servicing Asset at Fair Value, Amount $ 1,710 $ 1,572 $ 1,307