Fair Value Of Financial Instruments (Quantitative Information Regarding The Significant Unobservable Inputs For Certain Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - Variable Interest Entity Primary Beneficiary [Member] - Impact Of Financial Guarantee [Member] - USD ($) $ in Millions		Jun. 30, 2022	Dec. 31, 2021
Variable Interest Entity Notes [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities		$ 217	$ 291
Loans Receivable and Other Instruments at Fair Value [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, assets		$ 68	$ 77
Minimum [Member] | Variable Interest Entity Notes [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	39.00%	33.00%
Minimum [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	12.00%	23.00%
Maximum [Member] | Variable Interest Entity Notes [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	77.00%	73.00%
Maximum [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	82.00%	72.00%
Weighted Average [Member] | Variable Interest Entity Notes [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	66.00%	59.00%
Weighted Average [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	[1]	55.00%	55.00%

[1] Weighted average represents the total MBIA guarantees as a percentage of total instrument fair value.