Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	$ 95,261	$ 100,445
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	95,261	100,445
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	267	439
Retained interests in securitizations	41	55
Net derivative assets (liabilities)	19	31	$ 26	$ (10)
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	73,616	76,703
RMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	73,616	76,703
RMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	258	328
CMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	9,369	11,735
CMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	$ 9	$ 111
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	0.02
Yield | RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.21	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	0.03	0.03
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.01	0.01
Yield | CMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.02	0.03
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	0.01	0.02
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	0.03
Voluntary prepayment rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.18	0.13
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	0.05	0.08
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	0.40	0.15
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	0.11	0.10
Default rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.03	0.03
Default rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.04	0.03
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	0.01	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	0.11	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	0.72	0.55
Loss severity | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	1.51	0.70
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	0.30	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	1	1
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	0.65	0.73
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	29 months	37 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	36 months	52 months
Discount rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.02	0.02
Discount rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.08	0.12
Swap rates | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.01	0.01
Swap rates | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.02	0.01
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	0.02	0.01