Fair Value - Significant Unobservable Inputs Used in the Valuation of MSRs (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Minimum
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	6.50%	4.20%
Maturity (months)	20 months	6 months
Discount rate	9.50%	9.50%
Maximum
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Prepayment speed	13.50%	13.10%
Maturity (months)	104 months	92 months
Discount rate	12.00%	12.00%