Schedule I- Investments (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 3,343
Fair Value	3,462
Amount at which shown in the balance sheet	3,462
Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,125
Fair Value	1,111
Amount at which shown in the balance sheet	1,109
Loans Receivable [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	135
Fair Value	136
Amount at which shown in the balance sheet	136
Long-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,714
Fair Value	2,829
Amount at which shown in the balance sheet	2,829
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	640
Fair Value	685
Amount at which shown in the balance sheet	685
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	178
Fair Value	200
Amount at which shown in the balance sheet	200
Long-Term Available-For-Sale [Member] | Foreign Governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2
Fair Value	2
Amount at which shown in the balance sheet	2
Long-Term Available-For-Sale [Member] | Corporate Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,078
Fair Value	1,129
Amount at which shown in the balance sheet	1,129
Short-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	270
Fair Value	270
Amount at which shown in the balance sheet	270
AFS Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,984
Fair Value	3,099
Amount at which shown in the balance sheet	3,099
Investments At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	359
Fair Value	363
Amount at which shown in the balance sheet	363
Investments At Fair Value [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	100
Fair Value	83
Amount at which shown in the balance sheet	83
Held-To-Maturity [Member] | Corporate Obligations [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	890
Fair Value	892
Amount at which shown in the balance sheet	890
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	317
Fair Value	320
Amount at which shown in the balance sheet	320
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	23
Fair Value	19
Amount at which shown in the balance sheet	19
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	20
Fair Value	20
Amount at which shown in the balance sheet	20
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	139
Fair Value	137
Amount at which shown in the balance sheet	137
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	317
Fair Value	317
Amount at which shown in the balance sheet	$ 317