Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 75	$ 60
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	75	59
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	90	77
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		71
Fair value of derivative liabilities	89
Net Amount, Derivative Assets	75	59
Net Amount, Derivative Liabilities	1	6
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	90	77
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	52	66
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	52	66
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,657	1,712
Derivative Liabilities Gross Amount Of Collateral Cash And Securities Pledged Not Offset		0
Fair value of derivative liabilities	0
Net Amount, Derivative Assets	52	66
Net Amount, Derivative Liabilities	1,657	1,712
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	1,657	1,712
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	1
Net Amount, Derivative Liabilities	0	1
Derivative Liability, Fair Value, Gross Liability	0	1
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	75	60
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	75	59
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	90	72
Fair value of derivative liabilities	89	67
Net Amount, Derivative Assets	75	59
Net Amount, Derivative Liabilities	1	5
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Derivative Liability, Fair Value, Gross Liability	89	72
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Interest Rate Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,657	1,712
Net Amount, Derivative Liabilities	1,657	1,712
Derivative Liability, Fair Value, Gross Liability	1,657	1,712
Future [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities		3
Fair value of derivative liabilities		3
Net Amount, Derivative Liabilities		0
Derivative Liability, Fair Value, Gross Liability		3
Derivative Liability, Fair Value, Amount Offset Against Collateral		0
Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	52	66
Derivative Asset, Fair Value, Amount Offset Against Collateral	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	52	66
Net Amount, Derivative Assets	$ 52	66
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ 0