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MSR (Sales of Receivables and Servicing Rights - Additional Information) (Detail) - USD ($)
$ in Billions
 3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Transfers and Servicing of Financial Assets [Abstract]    
Servicing of residential mortgage loans for other investors $ 81.9 $ 80.7