Fair Value of Assets and Liabilities - Quantitative Information about Significant Unobservable Inputs Used for Fair Value Measurements (Detail)	6 Months Ended	12 Months Ended
	Jun. 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	0.074
Discount rates | 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	0.055
Discount rates | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.074
Discount rates | 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	0.066
Discount rates | Weighted- Average
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale	0.074
Discount rates | 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	0.058
Discount rates | Level 3 Inputs | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	8.60%	8.80%
Discount rates | Level 3 Inputs | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	7.50%	7.50%
Discount rates | Level 3 Inputs | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	16.70%	17.10%
Discount rates | Level 3 Inputs | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	16.40%	16.40%
Discount rates | Level 3 Inputs | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	12.70%	12.70%
Discount rates | Level 3 Inputs | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	9.90%	10.10%
Net cumulative expected loss rates | 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	0.072
Net cumulative expected loss rates | 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	0.091
Net cumulative expected loss rates | 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	0.083
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	2.20%	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	2.00%	2.10%
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	10.20%	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	36.40%	36.70%
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	6.30%	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	15.40%	15.60%
Cumulative expected prepayment rates | 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	0.330
Cumulative expected prepayment rates | 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	0.340
Cumulative expected prepayment rates | 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	0.334
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	22.00%	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	17.00%	15.80%
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	30.70%	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	47.70%	47.20%
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	27.30%	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	32.90%	35.90%