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Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 89,733	$ 83,013
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	89,733	83,013
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	126	118
Retained interests in securitizations	29	34
Net derivative assets (liabilities)	108	69
Total RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	68,899	65,328
Total RMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	68,899	65,328
Total RMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	126	116
CMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	8,440	7,825
CMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0	$ 2
Yield | Total RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.05	0.06
Yield | Total RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.10	0.10
Yield | Total RMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.06	0.06
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.04	0.05
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.04	0.07
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.04	0.07
Life of receivables (months) | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input, life of receivables	34 months	31 months
Life of receivables (months) | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input, life of receivables	68 months	81 months
Voluntary prepayment rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.08	0.07
Voluntary prepayment rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.08	0.09
Voluntary prepayment rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0	0
Voluntary prepayment rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.16	0.12
Voluntary prepayment rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.07	0.07
Discount rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.05	0.05
Discount rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.13	0.15
Default rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.01	0.01
Default rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.01	0.01
Default rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0	0
Default rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.06	0.06
Default rate | Total RMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.01	0.01
Loss severity | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.49	0.44
Loss severity | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.49	1.55
Loss severity | Total RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.25	0.25
Loss severity | Total RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.75	0.80
Loss severity | Total RMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.56	0.61
Swap rates | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.03	0.04
Swap rates | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.04	0.04
Swap rates | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.03	0.04

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