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Mortgage Banking Activities, Analysis of Changes in Amortized MSRs (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Changes in amortized MSRs    
Amortization $ (66) $ (66)
Amortized [Member]    
Changes in amortized MSRs    
Balance, beginning of period 1,430 1,443
Purchases 8 24
Servicing from securitizations or asset transfers 34 26
Amortization (66) (66)
Balance, end of period 1,406 1,427
Fair value of amortized MSRs:    
Beginning of period 1,872 2,288
End of period 1,490 2,149
Commercial mortgage servicing [Member] | Amortized [Member]    
Mortgage Banking Activities (Textual) [Abstract]    
Valuation allowance $ 0 $ 0