Fair Value Measurement (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	$ 12,718		$ 16,206
Fair value financial liabilities measured on recurring basis	7,329		10,946
Cash and Cash Equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	269		473
Cash			160
Variable Interest Entity [Member] | Cash and Cash Equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	145
Variable Interest Entity [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,903		2,046
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	40
Money Market Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	641		912
Money Market Securities [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	109		199
Perpetual Preferred Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	49		107
Medium-term Notes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	151		165
Total Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	7,093		8,682
Fixed-Maturity Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,373		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	2,121		3,117
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	311		239
Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Securities [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	821		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	417		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	369		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	203		303
Fixed-Maturity Investments [Member] | Taxable Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5,293		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	1,112		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	352		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	1,241		1,739
Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Securities [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,116		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	184		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	47		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	102		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	200		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	939		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	1,070		1,165
Total Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	30		35
Derivative Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	5		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	3
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	2		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	1		3
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)
Assets Of Consolidated VIEs [Member] | Loan Repurchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,032		1,077
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	3,302		4,808
Derivative Liabilities [Member] | Credit Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis			445
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	26		4
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	165		281
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		(93)
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	21		17
Other Liabilities [Member] | Warrant [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	25		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	3,638		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	2,298		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	269		473
Cash			160
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Variable Interest Entity [Member] | Cash and Cash Equivalents [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	145
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	641		912
Quoted Prices In Active Markets for Identical Assets (Level 1) [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	109		199
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	1,775		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	1,114		1,316
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	1,114		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	851		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	263		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
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Total Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	20		25
Significant Other Observable Inputs (Level 2) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	6,967		8,576
Fair value financial liabilities measured on recurring basis	2,100		2,651
Significant Other Observable Inputs (Level 2) [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	40
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	46		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	5,008		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	4,962		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	1,822		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	216		170
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Residential Mortgage-Backed Securities [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	811		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	405		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	229		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	161		236
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	3,907		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	261		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	77		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	1,143		1,531
Significant Other Observable Inputs (Level 2) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Securities [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,112		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	154		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	20		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	73		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	128		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	939		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	1,045		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	96		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	96		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	1		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] | Credit Derivatives [Member] | Non-Insured Derivatives [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis			445
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	124		4
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	165		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
Significant Other Observable Inputs (Level 2) [Member] | Other Liabilities [Member] | Warrant [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	25		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	1,771		1,865
Significant Unobservable Inputs (Level 3) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	3,551		4,638
Fair value financial liabilities measured on recurring basis	5,327		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	1,903		2,046
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
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	151	[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	310		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	297		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	299		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	95	[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	10	[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	12	[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	140	[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	42	[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	272		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	98	[1]	207
Significant Unobservable Inputs (Level 3) [Member] | Fixed-Maturity Investments [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Securities [Member] | Mortgage-Backed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	4	[1]	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	30	[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	27	[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	29	[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	72	[1]	317
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	25	[1]	28
Significant Unobservable Inputs (Level 3) [Member] | Total Other Investments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	10	[1]	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	7		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	3
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] | Assets Of Consolidated VIEs [Member] | Loan Repurchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	1,032		1,077
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	3,288		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] | Currency Derivatives [Member] | Variable Interest Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	21	[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	1,867		2,889
Counterparty And Cash Collateral Netting [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value financial assets measured on recurring basis	(98)		(93)
Fair value financial liabilities measured on recurring basis	(98)		(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	(98)		(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	(98)
Counterparty And Cash Collateral Netting [Member] | 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)
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	(98)
Counterparty And Cash Collateral Netting [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			$ (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.