Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 93	$ 75
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	93	75
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	114	90
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		89
Fair value of derivative liabilities	113
Net Amount, Derivative Assets	93	75
Net Amount, Derivative Liabilities	1	1
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	114	90
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	41	52
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	41	52
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,835	1,657
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		0
Fair value of derivative liabilities	0
Net Amount, Derivative Assets	41	52
Net Amount, Derivative Liabilities	1,835	1,657
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	1,835	1,657
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	0	0
Net Amount, Derivative Liabilities	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	93	75
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	93	75
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	114	90
Fair value of derivative liabilities	113	89
Net Amount, Derivative Assets	93	75
Net Amount, Derivative Liabilities	1	1
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Derivative Liability, Fair Value, Gross Liability	114	89
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,835	1,657
Net Amount, Derivative Liabilities	1,835	1,657
Derivative Liability, Fair Value, Gross Liability	1,835	1,657
Currency Swaps [Member] | Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	41	52
Derivative Asset, Fair Value, Amount Offset Against Collateral	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	41	52
Net Amount, Derivative Assets	$ 41	52
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 0