Fair Value of Assets and Liabilities - Quantitative Information about Significant Unobservable Inputs Used for Fair Value Measurements (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Level 3 Inputs | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Total market servicing rates (percent per annum on outstanding principal balance)	0.62%	0.62%
Level 3 Inputs | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Total market servicing rates (percent per annum on outstanding principal balance)	0.62%	0.62%
Level 3 Inputs | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Total market servicing rates (percent per annum on outstanding principal balance)	0.62%	0.62%
Discount rates | Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.077
Discount rates | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.077
Discount rates | Weighted- Average
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.077
Discount rates | Level 3 Inputs | Minimum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.088
Discount rates | Level 3 Inputs | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	8.80%
Discount rates | Level 3 Inputs | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	8.50%	8.80%
Discount rates | Level 3 Inputs | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	8.70%	7.50%
Discount rates | Level 3 Inputs | Maximum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.112
Discount rates | Level 3 Inputs | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	11.20%
Discount rates | Level 3 Inputs | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	16.50%	17.10%
Discount rates | Level 3 Inputs | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	17.30%	16.40%
Discount rates | Level 3 Inputs | Weighted- Average | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.095
Discount rates | Level 3 Inputs | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	9.60%
Discount rates | Level 3 Inputs | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	12.80%	12.70%
Discount rates | Level 3 Inputs | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	11.60%	10.10%
Net cumulative expected loss rates | Level 3 Inputs | Minimum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.036
Net cumulative expected loss rates | Level 3 Inputs | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	3.50%
Net cumulative expected loss rates | Level 3 Inputs | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	2.50%	2.10%
Net cumulative expected loss rates | Level 3 Inputs | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	3.50%	2.10%
Net cumulative expected loss rates | Level 3 Inputs | Maximum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.230
Net cumulative expected loss rates | Level 3 Inputs | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	23.40%
Net cumulative expected loss rates | Level 3 Inputs | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	11.00%	9.80%
Net cumulative expected loss rates | Level 3 Inputs | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	37.70%	36.70%
Net cumulative expected loss rates | Level 3 Inputs | Weighted- Average | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.093
Net cumulative expected loss rates | Level 3 Inputs | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	10.90%
Net cumulative expected loss rates | Level 3 Inputs | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	7.10%	5.70%
Net cumulative expected loss rates | Level 3 Inputs | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	15.60%	15.60%
Cumulative expected prepayment rates | Level 3 Inputs | Minimum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.277
Cumulative expected prepayment rates | Level 3 Inputs | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	27.70%
Cumulative expected prepayment rates | Level 3 Inputs | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	20.60%	26.20%
Cumulative expected prepayment rates | Level 3 Inputs | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	18.50%	15.80%
Cumulative expected prepayment rates | Level 3 Inputs | Maximum | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.373
Cumulative expected prepayment rates | Level 3 Inputs | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	37.30%
Cumulative expected prepayment rates | Level 3 Inputs | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	28.50%	35.30%
Cumulative expected prepayment rates | Level 3 Inputs | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	44.60%	47.20%
Cumulative expected prepayment rates | Level 3 Inputs | Weighted- Average | Other asset-backed securities related to Structured Program transactions
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.327
Cumulative expected prepayment rates | Level 3 Inputs | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	32.50%
Cumulative expected prepayment rates | Level 3 Inputs | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	25.20%	30.80%
Cumulative expected prepayment rates | Level 3 Inputs | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	32.70%	35.90%