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Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Fair value financial assets measured on recurring basis		$ 21,227
Fair value financial liabilities measured on recurring basis	14,862	13,575
Variable Interest Entity, Primary Beneficiary [Member] | Loans Receivable [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis		2,183
Variable Interest Entity, Primary Beneficiary [Member] | Loans Receivable [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		2,183
Loans Receivable [Member]
Fair value financial assets measured on recurring basis	2,320
Loans Receivable [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	2,320
Variable Interest Entity, Primary Beneficiary [Member] | Loan Repurchase Commitments [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis		835
Variable Interest Entity, Primary Beneficiary [Member] | Loan Repurchase Commitments [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		835
Loan Repurchase Commitments [Member]
Fair value financial assets measured on recurring basis	905
Loan Repurchase Commitments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	905
Variable Interest Entity, Primary Beneficiary [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis		828
Variable Interest Entity, Primary Beneficiary [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		583
Variable Interest Entity, Primary Beneficiary [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		245
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage-Backed Agency [Member]
Fair value financial assets measured on recurring basis		37
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage-Backed Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		37
Variable Interest Entity, Primary Beneficiary [Member] | Commercial Mortgage-Backed [Member]
Fair value financial assets measured on recurring basis		930
Variable Interest Entity, Primary Beneficiary [Member] | Commercial Mortgage-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		907
Variable Interest Entity, Primary Beneficiary [Member] | Commercial Mortgage-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		23
Variable Interest Entity, Primary Beneficiary [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis	4,970	5,431
Variable Interest Entity, Primary Beneficiary [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		11
Variable Interest Entity, Primary Beneficiary [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	4,590	4,949
Variable Interest Entity, Primary Beneficiary [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	380	471
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member]
Fair value financial assets measured on recurring basis	3
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Credit Derivatives [Member]
Fair value financial assets measured on recurring basis	1	687
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	1
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		687
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member]
Fair value financial assets measured on recurring basis	42	12
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	38	12
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	4
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Other Derivatives [Member]
Fair value financial assets measured on recurring basis	(40)
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Other Derivatives [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial assets measured on recurring basis	(40)
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	39
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	4
Variable Interest Entity, Primary Beneficiary [Member] | Derivative Assets [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial assets measured on recurring basis	(40)
Variable Interest Entity, Primary Beneficiary [Member] | State and Municipal Taxable Bonds [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis		4
Variable Interest Entity, Primary Beneficiary [Member] | State and Municipal Taxable Bonds [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		4
Variable Interest Entity, Primary Beneficiary [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Fair value financial assets measured on recurring basis		435
Variable Interest Entity, Primary Beneficiary [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		352
Variable Interest Entity, Primary Beneficiary [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		83
Variable Interest Entity, Primary Beneficiary [Member] | U.S. Treasury and Government Agency [Member]
Fair value financial assets measured on recurring basis		4
Variable Interest Entity, Primary Beneficiary [Member] | U.S. Treasury and Government Agency [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		4
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member]
Fair value financial assets measured on recurring basis		447
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		7
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		360
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		80
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage-Backed Non-Agency [Member]
Fair value financial assets measured on recurring basis		2,746
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		2,706
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		40
Variable Interest Entity, Primary Beneficiary [Member] | Credit Derivatives [Member]
Fair value financial liabilities measured on recurring basis	1,590	1,455
Variable Interest Entity, Primary Beneficiary [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis	1,590	1,455
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Derivatives [Member]
Fair value financial liabilities measured on recurring basis	554	635
Variable Interest Entity, Primary Beneficiary [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	554	635
Variable Interest Entity, Primary Beneficiary [Member] | Currency Derivatives [Member]
Fair value financial liabilities measured on recurring basis	16	14
Variable Interest Entity, Primary Beneficiary [Member] | Currency Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis	16	14
Variable Interest Entity, Primary Beneficiary [Member] | Variable Interest Entity Notes [Member]
Fair value financial liabilities measured on recurring basis	6,539	6,680
Variable Interest Entity, Primary Beneficiary [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	2,026	2,007
Variable Interest Entity, Primary Beneficiary [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis	4,513	4,673
Collateralized Debt Obligations [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member]
Fair value financial assets measured on recurring basis	286	299
Collateralized Debt Obligations [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	124	108
Collateralized Debt Obligations [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	162	191
Residential Mortgage-Backed Agency [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member]
Fair value financial assets measured on recurring basis	1,434	1,589
Residential Mortgage-Backed Agency [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	1,434	1,548
Residential Mortgage-Backed Agency [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		41
Commercial Mortgage-Backed [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member]
Fair value financial assets measured on recurring basis	91	161
Commercial Mortgage-Backed [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	41	120
Commercial Mortgage-Backed [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	50	41
Fixed-Maturity Investments [Member]
Fair value financial assets measured on recurring basis	10,849	11,925
Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Fair value financial assets measured on recurring basis	7,255
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Fair value financial assets measured on recurring basis	493	462
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	465	414
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	28	48
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Fair value financial assets measured on recurring basis	566	660
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	235	310
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	331	350
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | State and Municipal Bonds [Member]
Fair value financial assets measured on recurring basis		752
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		738
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		14
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member]
Fair value financial assets measured on recurring basis		8,304
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		1,324
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		6,038
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		942
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury and Government Agency [Member]
Fair value financial assets measured on recurring basis	942	1,064
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury and Government Agency [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	805	915
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury and Government Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	137	149
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member]
Fair value financial assets measured on recurring basis	395	469
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	330	409
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	52	49
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	13	11
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member]
Fair value financial assets measured on recurring basis	2,250	2,848
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	1
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	1,955	2,602
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	294	246
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	1,136
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	5,228
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	891
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State and Municipal Bonds [Member]
Fair value financial assets measured on recurring basis		2,823
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		2,787
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		36
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member]
Fair value financial assets measured on recurring basis	798
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	785
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Asset-Backed Securities [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	13
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member]
Fair value financial assets measured on recurring basis	2,623
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	2,591
Fixed-Maturity Investments [Member] | State and Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	32
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Tax-Exempt Bonds [Member]
Fair value financial assets measured on recurring basis	15	32
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		13
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	15	19
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Perpetual Preferred Securities [Member]
Fair value financial assets measured on recurring basis	170
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Perpetual Preferred Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	170
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Other Investments: [Member]
Fair value financial assets measured on recurring basis	32
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Other Investments: [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	32
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Money Market Securities [Member]
Fair value financial assets measured on recurring basis	754
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Money Market Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	754
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member]
Fair value financial assets measured on recurring basis	9,893	11,159
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	1,136	1,337
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	7,834	8,844
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	923	978
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	1,922	1,906
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	8,004	9,041
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	923	978
Assets of Consolidated VIEs [Member] | Corporate Obligations [Member]
Fair value financial assets measured on recurring basis	279
Assets of Consolidated VIEs [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	219
Assets of Consolidated VIEs [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	60
Derivative Assets [Member]
Fair value financial assets measured on recurring basis	19,872	4
Derivative Assets [Member] | Credit Derivatives [Member]
Fair value financial assets measured on recurring basis		3
Derivative Assets [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		3
Derivative Assets [Member] | Interest Rate Derivatives [Member]
Fair value financial assets measured on recurring basis		62
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		57
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		5
Derivative Assets [Member] | Other Derivatives [Member]
Fair value financial assets measured on recurring basis		(61)
Derivative Assets [Member] | Other Derivatives [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial assets measured on recurring basis		(61)
Derivative Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	2,067
Derivative Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	12,643	60
Derivative Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	5,202	5
Derivative Assets [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial assets measured on recurring basis	(40)	(61)
Derivative Liabilities [Member] | Credit Derivatives [Member]
Fair value financial liabilities measured on recurring basis		4,375
Derivative Liabilities [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis		25
Derivative Liabilities [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis		4,350
Derivative Liabilities [Member] | Interest Rate Derivatives [Member]
Fair value financial liabilities measured on recurring basis		297
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis		297
Derivative Liabilities [Member] | Currency Derivatives [Member]
Fair value financial liabilities measured on recurring basis		6
Derivative Liabilities [Member] | Currency Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis		6
Derivative Liabilities [Member] | Other Derivatives [Member]
Fair value financial liabilities measured on recurring basis		(61)
Derivative Liabilities [Member] | Other Derivatives [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial liabilities measured on recurring basis		(61)
Derivative Liabilities [Member] | Warrants [Member]
Fair value financial liabilities measured on recurring basis		58
Derivative Liabilities [Member] | Warrants [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis		58
Other Liabilities [Member] | Warrants [Member]
Fair value financial liabilities measured on recurring basis	23
Other Liabilities [Member] | Warrants [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	23
Tax-Exempt Bonds [Member] | Perpetual Preferred Securities [Member]
Fair value financial assets measured on recurring basis		192
Tax-Exempt Bonds [Member] | Perpetual Preferred Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		192
Tax-Exempt Bonds [Member] | Other Investments: [Member]
Fair value financial assets measured on recurring basis		21
Tax-Exempt Bonds [Member] | Other Investments: [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		16
Tax-Exempt Bonds [Member] | Other Investments: [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		5
Tax-Exempt Bonds [Member]
Fair value financial assets measured on recurring basis		553
Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		553
Residential Mortgage-Backed Agency [Member]
Fair value financial assets measured on recurring basis	13
Residential Mortgage-Backed Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	13
Residential Mortgage-Backed Non-Agency [Member]
Fair value financial assets measured on recurring basis	2,617
Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	2,600
Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	17
Commercial Mortgage-Backed [Member]
Fair value financial assets measured on recurring basis	836
Commercial Mortgage-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	809
Commercial Mortgage-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	27
Collateralized Debt Obligations [Member]
Fair value financial assets measured on recurring basis	858
Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	657
Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	201
Other Asset-Backed [Member]
Fair value financial assets measured on recurring basis	367
Other Asset-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	292
Other Asset-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	75
Money Market Securities [Member]
Fair value financial assets measured on recurring basis	145	150
Money Market Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis	145	150
Credit Derivatives [Member]
Fair value financial assets measured on recurring basis	670
Credit Derivatives [Member] | Insured Derivatives [Member]
Fair value financial liabilities measured on recurring basis	5,676
Credit Derivatives [Member] | Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	20
Credit Derivatives [Member] | Insured Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis	5,656
Credit Derivatives [Member] | Non-Insured Derivatives [Member]
Fair value financial liabilities measured on recurring basis	2
Credit Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	2
Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis	670
Interest Rate Derivatives [Member]
Fair value financial assets measured on recurring basis	10
Fair value financial liabilities measured on recurring basis	285
Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis	10
Fair value financial liabilities measured on recurring basis	285
Currency Derivatives [Member]
Fair value financial liabilities measured on recurring basis	11
Currency Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value financial liabilities measured on recurring basis	11
Other Derivatives [Member]
Fair value financial liabilities measured on recurring basis	(40)
Other Derivatives [Member] | Counterparty and Cash Collateral Netting [Member]
Fair value financial liabilities measured on recurring basis	(40)
Medium-term Notes [Member]
Fair value financial liabilities measured on recurring basis	206	116
Medium-term Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value financial liabilities measured on recurring basis	206	116
Fair Value, Inputs, Level 1 [Member]
Fair value financial assets measured on recurring basis		2,067
Fair Value, Inputs, Level 2 [Member]
Fair value financial assets measured on recurring basis		14,062
Fair value financial liabilities measured on recurring basis	2,921	3,028
Fair Value, Inputs, Level 3 [Member]
Fair value financial assets measured on recurring basis		5,159
Fair value financial liabilities measured on recurring basis	11,981	10,608
Counterparty and Cash Collateral Netting [Member]
Fair value financial assets measured on recurring basis		(61)
Fair value financial liabilities measured on recurring basis	$ (40)	$ (61)

X

- Definition

Fair Value Liabilities Measured On Recurring Basis

+ Details

Name:	mbi_FairValueLiabilitiesMeasuredOnRecurringBasis
Namespace Prefix:	mbi
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 12
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 7
-Section 03
-Paragraph 1
-Subparagraph a, f, g

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6956420&loc=d3e24584-111560

+ Details

Name:	us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant