Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	$ 15,573	$ 21,227
Fair value financial liabilities measured on recurring basis	10,946	13,575
Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,452	2,067
Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	8,576	14,062
Fair value financial liabilities measured on recurring basis	2,651	3,028
Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4,638	5,159
Fair value financial liabilities measured on recurring basis	8,388	10,608
Counterparty And Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(93)	(61)
Fair value financial liabilities measured on recurring basis	(93)	(61)
Perpetual Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	107	192
Perpetual Preferred Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	106	192
Perpetual Preferred Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1
Other Long Term Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	35	21
Other Long Term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	25	16
Other Long Term Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		5
Other Long Term Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	10
Money Market Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	912	553
Money Market Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	912	553
Medium-Term Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	165	116
Medium-Term Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	165	116
Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	8,682	11,925
Total Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,253	1,906
Total Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5,746	9,041
Total Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	683	978
Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	7,628	11,159
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,316	1,337
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5,640	8,844
Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	672	978
Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,448	8,304
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,316	1,324
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4,488	6,038
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	644	942
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	1,141	1,064
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,038	915
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	103	149
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	350	469
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	277	409
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	62	49
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Foreign Governments [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	11	11
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	1,738	2,848
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
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]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,531	2,602
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	206	246
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	924	752
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | State And Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	924	738
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | State And Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		14
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,284	1,589
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,276	1,548
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	8	41
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	367	462
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	350	414
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	17	48
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	58	161
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	34	120
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	24	41
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	138	299
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	78	108
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	60	191
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	448	660
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	130	310
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	318	350
Fixed-Maturity Investments [Member] | State And Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,165	2,823
Fixed-Maturity Investments [Member] | State And Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,137	2,787
Fixed-Maturity Investments [Member] | State And Municipal Taxable Bonds [Member] | Tax-Exempt Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	28	36
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	15	32
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		13
Fixed-Maturity Investments [Member] | Other Fixed Maturity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	15	19
Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2	4
Derivative Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	92	60
Derivative Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	5
Derivative Assets [Member] | Counterparty And Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(93)	(61)
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	3
Derivative Assets [Member] | Credit Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1	3
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	94	62
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	91	57
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	5
Derivative Assets [Member] | Other Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(93)	(61)
Derivative Assets [Member] | Other Derivatives [Member] | Non-Insured Derivatives [Member] | Counterparty And Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(93)	(61)
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	4,808	4,375
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	18	25
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	4,790	4,350
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	445	297
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	445	297
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	4	6
Derivative Liabilities [Member] | Currency Derivatives [Member] | Non-Insured Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	4	6
Derivative Liabilities [Member] | Other Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	(93)	(61)
Derivative Liabilities [Member] | Other Derivatives [Member] | Non-Insured Derivatives [Member] | Counterparty And Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	(93)	(61)
Other Liabilities [Member] | Warrants [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	38	58
Other Liabilities [Member] | Warrants [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	38	58
Variable Interest Entities [Member] | Money Market Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	199	150
Variable Interest Entities [Member] | Money Market Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	199	150
Variable Interest Entities [Member] | Variable Interest Entity Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	4,754
Variable Interest Entities [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	1,865
Variable Interest Entities [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	2,889
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3,117	5,431
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		11
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,735	4,949
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	382	471
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | U.S. Treasury And Government Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		4
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | U.S. Treasury And Government Agency [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		4
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	239	449
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		7
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	170	360
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	69	82
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | State And Municipal Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		4
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | State And Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis		4
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	37
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	37
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,458	2,746
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,437	2,706
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	21	40
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	581	930
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	559	907
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	22	23
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	533	828
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	330	583
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	203	245
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	303	433
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	236	352
Variable Interest Entities [Member] | Fixed-Maturity Investments [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	67	81
Variable Interest Entities [Member] | Derivative Assets [Member] | Credit Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	447	687
Variable Interest Entities [Member] | Derivative Assets [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	447	687
Variable Interest Entities [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	12
Variable Interest Entities [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3	12
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	527	1,455
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	527	1,455
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	281	635
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	281	635
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Currency Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	17	14
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Currency Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	17	14
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Variable Interest Entity Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		6,680
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		2,007
Variable Interest Entities [Member] | Derivative Liabilities [Member] | Variable Interest Entity Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		4,673
Loans Receivable [Member] | Variable Interest Entities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,046	2,183
Loans Receivable [Member] | Variable Interest Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	2,046	2,183
Loan Repurchase Commitments [Member] | Variable Interest Entities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,077	835
Loan Repurchase Commitments [Member] | Variable Interest Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	$ 1,077	$ 835