Servicing Activities - Total Servicing Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Loan Servicing Portfolio [Abstract]
MSRs, UPB	$ 129,024	$ 148,155
MSRs, Fair Value	483	476
Capitalized MSRs owned
Loan Servicing Portfolio [Abstract]
MSRs, UPB	7,121	8,592
MSRs, Fair Value	46	57
Capitalized MSRs under secured borrowing arrangements and subserviced
Loan Servicing Portfolio [Abstract]
MSRs, UPB	45,770	49,193
MSRs, Fair Value	437	419
Capitalized MSRs
Loan Servicing Portfolio [Abstract]
MSRs, UPB	52,891	57,785
MSRs, Fair Value	483	476
Subserviced
Loan Servicing Portfolio [Abstract]
MSRs, UPB	75,810	89,844
Other servicing
Loan Servicing Portfolio [Abstract]
MSRs, UPB	$ 323	$ 526