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