Schedule I- Investments (Detail) $ in Millions	Dec. 31, 2021 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 2,639
Fair Value	2,793
Amount at which shown in the balance sheet	2,793
Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	176
Fair Value	137
Amount at which shown in the balance sheet	137
Loans Receivable [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	108
Fair Value	77
Amount at which shown in the balance sheet	77
Long-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,018
Fair Value	2,159
Amount at which shown in the balance sheet	2,159
Long-Term Available-For-Sale [Member] | U.S. Treasury And Government Agency [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	515
Fair Value	566
Amount at which shown in the balance sheet	566
Long-Term Available-For-Sale [Member] | US States And Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	140
Fair Value	167
Amount at which shown in the balance sheet	167
Long-Term Available-For-Sale [Member] | Foreign Governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	11
Fair Value	11
Amount at which shown in the balance sheet	11
Long-Term Available-For-Sale [Member] | Corporate Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	881
Fair Value	930
Amount at which shown in the balance sheet	930
Short-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	298
Fair Value	298
Amount at which shown in the balance sheet	298
AFS Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,316
Fair Value	2,457
Amount at which shown in the balance sheet	2,457
Investments At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	323
Fair Value	336
Amount at which shown in the balance sheet	336
Investments At Fair Value [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	68
Fair Value	60
Amount at which shown in the balance sheet	60
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Residential Mortgage Backed Agency [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	190
Fair Value	192
Amount at which shown in the balance sheet	192
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Residential Mortgage-Backed Non-Agency [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	80
Fair Value	92
Amount at which shown in the balance sheet	92
Mortgage-backed [Member] | Long-Term Available-For-Sale [Member] | Commercial Mortgage-Backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10
Fair Value	10
Amount at which shown in the balance sheet	10
Asset-backed [Member] | Long-Term Available-For-Sale [Member] | Collateralized Debt Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	101
Fair Value	101
Amount at which shown in the balance sheet	101
Asset-backed [Member] | Long-Term Available-For-Sale [Member] | Other Asset-Backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	90
Fair Value	90
Amount at which shown in the balance sheet	$ 90