Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	$ 89,076	$ 95,261
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	89,076	95,261
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	232	267
Retained interests in securitizations	39	41
Net derivative assets (liabilities)	22	19	$ 34	$ 31
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	68,425	73,616
RMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	68,425	73,616
RMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	211	258
CMBS | Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	8,365	9,369
CMBS | Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available for sale	$ 21	$ 9
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
Yield | RMBS | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Securities available-for-sale, measurement input	0.25	0.21
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	0.04	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	0.23	0.02
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	0.15	0.01
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	0.18	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	0.05	0.05
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	0.20	0.40
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	0.11
Default rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.01	0.03
Default rate | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.03	0.04
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	0.01
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	0.76	0.72
Loss severity | Recurring | Level 3 | Discounted cash flows | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	2.91	1.51
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	0.88	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	0.63	0.65
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	29 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	37 months	36 months
Discount rate | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Retained interests, measurement input	0.03	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	0.08
Swap rates | Recurring | Level 3 | Discounted cash flows | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative assets (liabilities), measurement input	0.02	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	0.02
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	0.02