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Mortgage Servicing Assets - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Commercial Mortgage Backed Securities    
Servicing Assets at Fair Value [Line Items]    
Contractual fee income from servicing commercial mortgage loans $ 61 $ 50
Amortization of servicing commercial mortgage loans (29) (29)
Residential mortgage-backed securities    
Servicing Assets at Fair Value [Line Items]    
Contractual fee income from servicing commercial mortgage loans 10 6
Amortization of servicing commercial mortgage loans $ (5) $ (2)