Fair Value Measurements - Quantitative Information about Significant Unobservable Inputs Used for Fair Value Measurements (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Level 3 | 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 | 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 | 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 rate | Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale		0.070
Discount rate | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale		0.070
Discount rate | Weighted- Average
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, debt securities available-for-sale		0.070
Discount rate | Level 3 | 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		0.081
Discount rate | Level 3 | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		8.10%	5.00%
Discount rate | Level 3 | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	8.80%	8.40%
Discount rate | Level 3 | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		8.70%	7.50%
Discount rate | Level 3 | 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		0.103
Discount rate | Level 3 | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		10.30%	12.60%
Discount rate | Level 3 | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	17.10%	16.20%
Discount rate | Level 3 | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		17.30%	16.40%
Discount rate | Level 3 | 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		0.090
Discount rate | Level 3 | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		9.00%	9.10%
Discount rate | Level 3 | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	12.70%	12.80%
Discount rate | Level 3 | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		11.30%	10.10%
Annualized net charge-off rate | Level 3 | 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		0.049
Annualized net charge-off rate | Level 3 | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		2.70%	1.90%
Annualized net charge-off rate | Level 3 | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	1.60%	1.90%
Annualized net charge-off rate | Level 3 | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		1.90%	1.30%
Annualized net charge-off rate | Level 3 | 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		0.059
Annualized net charge-off rate | Level 3 | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		12.90%	23.20%
Annualized net charge-off rate | Level 3 | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	5.30%	5.90%
Annualized net charge-off rate | Level 3 | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		24.00%	23.70%
Annualized net charge-off rate | Level 3 | 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		0.055
Annualized net charge-off rate | Level 3 | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		6.50%	11.60%
Annualized net charge-off rate | Level 3 | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	3.20%	3.70%
Annualized net charge-off rate | Level 3 | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		8.70%	9.30%
Annualized prepayment rate | Level 3 | 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		0.192
Annualized prepayment rate | Level 3 | Minimum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		15.70%	18.50%
Annualized prepayment rate | Level 3 | Minimum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	19.50%	18.60%
Annualized prepayment rate | Level 3 | Minimum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		15.60%	16.30%
Annualized prepayment rate | Level 3 | 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		0.210
Annualized prepayment rate | Level 3 | Maximum | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		22.50%	27.70%
Annualized prepayment rate | Level 3 | Maximum | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	31.00%	27.70%
Annualized prepayment rate | Level 3 | Maximum | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		25.70%	30.90%
Annualized prepayment rate | Level 3 | 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		0.201
Annualized prepayment rate | Level 3 | Weighted- Average | Loans Held For Sale
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		19.90%	22.90%
Annualized prepayment rate | Level 3 | Weighted- Average | Loans Held for Investment
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent	24.00%	22.60%
Annualized prepayment rate | Level 3 | Weighted- Average | Servicing Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Measurement input, percent		20.30%	24.40%