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Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Detail) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Asset-backed Securities [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | $ 66 | $ 72 | $ 72 | $ 72
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 0 | 0 |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings | 0 | 0 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | (6) | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0 | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances | 0 | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 0 | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 | 0 |  |
Interest Rate Swap [Member] | Interest Rate Swap [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 79 | 54 | 67 | 47
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 13 | 8 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 13 | 8 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (1) | (1) |  |
Credit Derivative [Member] | Credit Derivative [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | (2) | (1) | 0 | (1)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | (2) | 0 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | (1) | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | 0 | 0 |  |
Derivative [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 77 | 53 | 66 | 46
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 12 | 8 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 12 | 8 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (1) | (1) |  |
Level 3 [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 5,884 | 7,139 | 6,207 | 6,930
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 129 | 166 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | (377) |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 130 | 160 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | (377) | 135 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (76) | (87) |  |
Level 3 [Member] | Asset-backed Securities [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | (6) |  |  |
Level 3 [Member] | Investments [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 66 | 72 | 72 | 72
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | (6) |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 0 | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | (6) | 0 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | 0 | 0 |  |
Level 3 [Member] | Other Assets [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 3 | 4 | 3 | 5
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 0 | 0 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | 0 |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 0 | 0 |  |
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 77 | 53 | 66 | 46
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 12 | 8 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | 0 |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 12 | 8 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (1) | (1) |  |
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Long-term Debt [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 0 | (224) | 0 | (217)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 0 | 3 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | 0 |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 0 | (3) |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | 0 | (4) |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | 0 | 0 |  |
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Loans Receivable [Member] | Loans [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 2,932 | 4,376 | 3,108 | 4,288
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 88 | 88 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | (190) |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 88 | 88 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | (190) | 85 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements | (74) | (85) |  |
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Corporate Debt Securities [Member] | Investments Contract [Member] |  |  |  |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability | 2,806 | 2,858 | $ 2,957 | $ 2,737
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | 30 | 67 |  |
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI | (181) |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings | 30 | 67 |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss | $ (181) | $ 54 |  |

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