Schedule I- Investments (Detail) $ in Millions	Dec. 31, 2016 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 5,648
Fair Value	5,633
Amount at which shown in the balance sheet	5,633
Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,677
Fair Value	2,197
Amount at which shown in the balance sheet	2,211
Other Aggregated Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3
Fair Value	3
Amount at which shown in the balance sheet	3
Loans Receivable [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	589
Fair Value	1,066
Amount at which shown in the balance sheet	1,066
Long-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	4,839
Fair Value	4,819
Amount at which shown in the balance sheet	4,819
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	843
Fair Value	863
Amount at which shown in the balance sheet	863
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	1,382
Fair Value	1,439
Amount at which shown in the balance sheet	1,439
Long-Term Available-For-Sale [Member] | Foreign Governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5
Fair Value	5
Amount at which shown in the balance sheet	5
Long-Term Available-For-Sale [Member] | Corporate Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,332
Fair Value	1,250
Amount at which shown in the balance sheet	1,250
Short-Term Available-For-Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	607
Fair Value	607
Amount at which shown in the balance sheet	607
Equity Available For Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	4
Fair Value	5
Amount at which shown in the balance sheet	5
AFS Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,450
Fair Value	5,431
Amount at which shown in the balance sheet	5,431
Investments At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	195
Fair Value	199
Amount at which shown in the balance sheet	199
Investments At Fair Value [Member] | Assets Of Consolidated VIEs [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	198
Fair Value	255
Amount at which shown in the balance sheet	255
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	876
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	871
Fair Value	862
Amount at which shown in the balance sheet	862
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	50
Fair Value	45
Amount at which shown in the balance sheet	45
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	41
Fair Value	41
Amount at which shown in the balance sheet	41
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	22
Fair Value	22
Amount at which shown in the balance sheet	22
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	293
Fair Value	292
Amount at which shown in the balance sheet	$ 292