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Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	$ 12,267			$ 16,206
Fair value financial liabilities measured on recurring basis	7,324			10,946
Cash And Cash Equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	298			473
Variable Interest Entity [Member] | Cash [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	143			160
Variable Interest Entity [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,892			2,046
Fair value financial assets measured on recurring basis	1,892
Variable Interest Entity [Member] | Loan Repurchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,051			1,077
Fair value financial assets measured on recurring basis	1,051
Money Market Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	593			912
Perpetual Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	31			107
Medium-Term Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	168			165
Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,683			8,682
Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,028			7,628
Fixed-Maturity Investments [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,196			3,316
Fixed-Maturity Investments [Member] | Other Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	10			15
Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	302			239
Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Agency [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				3
Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	860			1,458
Fixed-Maturity Investments [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	422			581
Fixed-Maturity Investments [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	364			533
Fixed-Maturity Investments [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	192			303
Fixed-Maturity Investments [Member] | State And Municipal Bonds [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	41
Fixed-Maturity Investments [Member] | Money Market Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	15			199
Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5,070			6,448
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	961			1,141
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	341			350
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,228			1,739
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,073			1,284
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	176			367
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	49			58
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	94			138
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	189			447
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	959			924
Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	948			1,165
Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	31
Fair value financial assets measured on recurring basis				35
Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4			2
Derivative Assets [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1
Derivative Assets [Member] | Credit Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				1
Derivative Assets [Member] | Credit Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				447
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3			94
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				3
Derivative Assets [Member] | Other [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				(93)
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	3,332			4,808
Derivative Liabilities [Member] | Credit Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				527
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	(2)			445
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	157			281
Derivative Liabilities [Member] | Other [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				(93)
Derivative Liabilities [Member] | Currency Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	2			4
Derivative Liabilities [Member] | Currency Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	23			17
Other Liabilities [Member] | Warrants [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	18			38
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	3,626			4,754
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,187			3,085
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Cash And Cash Equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	298			473
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Variable Interest Entity [Member] | Cash [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	143			160
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Money Market Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	593			912
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,731			2,253
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,118			1,316
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	15			199
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Money Market Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	15			199
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,118			1,316
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	860			1,038
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	257			277
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1			1
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	20
Fair value financial assets measured on recurring basis				25
Significant Other Observable Inputs (Level 2) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,534			8,576
Fair value financial liabilities measured on recurring basis	2,236			2,651
Significant Other Observable Inputs (Level 2) [Member] | Perpetual Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	28			106
Significant Other Observable Inputs (Level 2) [Member] | Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4,601			5,746
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4,573			5,640
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,838			2,735
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Other Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	10			15
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	219			170
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Agency [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				3
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	852			1,437
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	409			559
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	191			330
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	126			236
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | State And Municipal Bonds [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	41
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3,638			4,488
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	101			103
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	72			62
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,136			1,531
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,073			1,276
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	169			350
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	19			34
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	64			78
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	116			130
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	888			924
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	925			1,137
Significant Other Observable Inputs (Level 2) [Member] | Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	95			92
Significant Other Observable Inputs (Level 2) [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				1
Significant Other Observable Inputs (Level 2) [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	95			91
Significant Other Observable Inputs (Level 2) [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				3
Significant Other Observable Inputs (Level 2) [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	14			18
Significant Other Observable Inputs (Level 2) [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	305			445
Significant Other Observable Inputs (Level 2) [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	157			281
Significant Other Observable Inputs (Level 2) [Member] | Derivative Liabilities [Member] | Currency Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1			4
Significant Other Observable Inputs (Level 2) [Member] | Other Liabilities [Member] | Warrants [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	18			38
Significant Other Observable Inputs (Level 2) [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1,741			1,865
Significant Unobservable Inputs (Level 3) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3,642			4,638
Fair value financial assets measured on recurring basis	3,637		3,544	4,188	4,309	4,528	4,467
Fair value financial liabilities measured on recurring basis	5,399			8,388
Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,892			2,046
Fair value financial assets measured on recurring basis	1,892		1,903	2,046	2,218	2,320	2,183
Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity [Member] | Loan Repurchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,051			1,077
Fair value financial assets measured on recurring basis	1,051		1,032	1,077	938	905	835
Significant Unobservable Inputs (Level 3) [Member] | Foreign Governments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	12		12	11	11	13	11
Significant Unobservable Inputs (Level 3) [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	91		98	207	342	294	246
Significant Unobservable Inputs (Level 3) [Member] | Corporate Obligations [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	83		95	69	63	62	82
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-Backed Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis			4	8	1		41
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-Backed Non-Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	7		33	17	27	28	48
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-Backed Non-Agency [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	8		10	21	15	17	40
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage-Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	30		27	24	32	50	41
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage-Backed [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	13		12	22	17	27	23
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Debt Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	30		29	60	67	162	192
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Debt Obligations [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	173		140	203	206	201	245
Significant Unobservable Inputs (Level 3) [Member] | Other Asset-Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	73		69	317	270	331	349
Significant Unobservable Inputs (Level 3) [Member] | Other Asset-Backed [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	66		42	67	71	73	81
Significant Unobservable Inputs (Level 3) [Member] | Perpetual Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	[1]		1
Fair value financial assets measured on recurring basis	3		3	1	1
Significant Unobservable Inputs (Level 3) [Member] | Medium-Term Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	168	[1]		165
Significant Unobservable Inputs (Level 3) [Member] | Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	351			683
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	337			672
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	343			382
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	83	[1]		69
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	8	[1]		21
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	13	[1]		22
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	173	[1]		203
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	66	[1]		67
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	314			644
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	12	[1]		11
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	91	[1]		207
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				8
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Non-Agency [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	7	[1]		17
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Commercial Mortgage-Backed [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	30	[1]		24
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Collateralized Debt Obligations [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	30	[1]		60
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Other Asset-Backed [Member] | Asset-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	73	[1]		317
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	71	[1]
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Tax-Exempt Bonds [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	23	[1]		28
Significant Unobservable Inputs (Level 3) [Member] | Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	11	[1]
Fair value financial assets measured on recurring basis				10
Significant Unobservable Inputs (Level 3) [Member] | Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5			3
Significant Unobservable Inputs (Level 3) [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1
Significant Unobservable Inputs (Level 3) [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				447
Significant Unobservable Inputs (Level 3) [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4	[1]		3
Significant Unobservable Inputs (Level 3) [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	3,318			4,790
Significant Unobservable Inputs (Level 3) [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				527
Significant Unobservable Inputs (Level 3) [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	4	[1]
Significant Unobservable Inputs (Level 3) [Member] | Derivative Liabilities [Member] | Currency Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1	[1]
Significant Unobservable Inputs (Level 3) [Member] | Derivative Liabilities [Member] | Currency Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	23	[1]		17
Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1,885			2,889
Counterparty and Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(96)			(93)
Fair value financial liabilities measured on recurring basis	(311)			(93)
Counterparty and Cash Collateral Netting [Member] | Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(96)			(93)
Counterparty and Cash Collateral Netting [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(96)
Counterparty and Cash Collateral Netting [Member] | Derivative Assets [Member] | Other [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis				(93)
Counterparty and Cash Collateral Netting [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	(311)
Counterparty and Cash Collateral Netting [Member] | Derivative Liabilities [Member] | Other [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				$ (93)
[1] Unobservable inputs are either not developed by the Company or do not significantly impact the overall fair values of the aggregate financial assets and liabilities.

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+ References

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

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- 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 Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558



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-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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7



Reference 5: 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



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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 12

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-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.



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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=16383099&loc=d3e24584-111560

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