Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	$ 74,837	$ 76,919
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	74,837	76,919
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	275	378
Retained interests in securitizations	35	36
Net derivative assets (liabilities)	68	5	$ 64	$ (5)	$ (12)	$ 19
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	59,882	62,589
RMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	59,882	62,589
RMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	149	236
CMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	7,839	7,870
CMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $87.7 billion and $87.0 billion and allowance for credit losses of $4 million and $3 million as of September 30, 2023 and December 31, 2022, respectively)	$ 126	$ 142
Yield | RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.03	0.03
Yield | RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.15	0.12
Yield | RMBS | Recurring | Level 3 | Discounted cash flows | Weighted average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.08	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	0.04
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	0.05
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
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	0.11	0.18
Voluntary prepayment rate | RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0	0.04
Voluntary prepayment rate | 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	0.20
Voluntary prepayment rate | 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	0.08
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	0.02	0.01
Default rate | 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 | 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	0.11
Default rate | 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	0.02
Loss severity | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.39	0.62
Loss severity | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	1.63	2.91
Loss severity | RMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.20	0.30
Loss severity | 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 | 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	0.58
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	33 months	30 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	64 months	43 months
Discount rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.05	0.04
Discount rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.13	0.07
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	0.04
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	0.04	0.04