Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 78,398	$ 79,117
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	78,398	79,117
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	438	278
Retained interests in securitizations	35	35
Net derivative assets (liabilities)	54	58
Total RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	62,398	63,638
Total RMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	62,398	63,638
Total RMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	309	146
CMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	8,193	8,323
CMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 129	$ 132
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	0.02
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	0.14	0.19
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	0.07
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.06	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	0.07	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	0.06	0.05
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	31 months	33 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	73 months	69 months
Voluntary prepayment rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.09	0.09
Voluntary prepayment rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.09	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	0.12	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	0.14
Default rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.01	0.02
Default rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.01	0.02
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	0.10	0.10
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	0.02	0.01
Loss severity | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.54	0.53
Loss severity | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	1.55	1.63
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	0.30	0.30
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	0.80	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	0.61	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	0.04	0.03
Swap rates | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.05	0.05
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	0.04	0.04