Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions		Dec. 31, 2016		Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		$ 7,564		$ 9,503
Fair value financial liabilities measured on recurring basis		1,784		2,918
Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		404		396
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		27		50
Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		149		172
Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		52		672
Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		8		14
Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		19		24
Money Market Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		521		354
Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		916		1,185
Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Other Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		150		107
Medium Term Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		101		161
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		1,351		2,362
Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		35		35
Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		163		464
Cash And Cash Equivalents [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		24		58
Fixed Income Funds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[1]	75		173
Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		4,999		5,785
Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		937		976
Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,440		1,726
Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		9		198
Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,334		1,457
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		868		993
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		45		51
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		43		31
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		22		34
Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		301		319
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		3		3
Derivative Assets [Member] | Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		19		11
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		66		88
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		213		208
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				45
Derivative Liabilities [Member] | Other Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		20		18
Other Liabilities [Member] | Warrant [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		33		18
Other Liabilities [Member] | Securities Sold Not Yet Purchased [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				18
Fair Value Inputs Level 1 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,559		1,913
Fair value financial liabilities measured on recurring basis		0		18
Fair Value Inputs Level 1 [Member] | Money Market Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		521		354
Fair Value Inputs Level 1 [Member] | Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		26		18
Fair Value Inputs Level 1 [Member] | Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		163		464
Fair Value Inputs Level 1 [Member] | Cash And Cash Equivalents [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		24		58
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		825		1,019
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		825		866
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis				153
Fair Value Inputs Level 1 [Member] | Other Liabilities [Member] | Securities Sold Not Yet Purchased [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				18
Fair Value Inputs Level 2 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		4,378		5,584
Fair value financial liabilities measured on recurring basis		1,123		1,401
Fair Value Inputs Level 2 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		27		39
Fair Value Inputs Level 2 [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		149		172
Fair Value Inputs Level 2 [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		52		672
Fair Value Inputs Level 2 [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		7		13
Fair Value Inputs Level 2 [Member] | Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		18		18
Fair Value Inputs Level 2 [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		875		1,095
Fair Value Inputs Level 2 [Member] | Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		9		17
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		4,113		4,649
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		112		110
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,440		1,685
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		9		43
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,332		1,450
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		868		993
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		45		51
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		43		31
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		7		5
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		257		281
Fair Value Inputs Level 2 [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		3		4
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		2		3
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		213		240
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				45
Fair Value Inputs Level 2 [Member] | Other Liabilities [Member] | Warrant [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		33		18
Fair Value Inputs Level 3 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,552		1,834
Fair value financial liabilities measured on recurring basis		661		1,531
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		404		396
Fair Value Inputs Level 3 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]			11
Fair Value Inputs Level 3 [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	1		1
Fair Value Inputs Level 3 [Member] | Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	1		6
Fair Value Inputs Level 3 [Member] | Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		916		1,185
Fair Value Inputs Level 3 [Member] | Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Other Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		150	[2]	107
Fair Value Inputs Level 3 [Member] | Medium Term Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis	[2]	101		161
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		476		1,267
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		61		117
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]			41
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]			2
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	2		7
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	15		29
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	44		38
Fair Value Inputs Level 3 [Member] | Derivative Assets [Member] | Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[2]	19		11
Fair Value Inputs Level 3 [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		64		85
Fair Value Inputs Level 3 [Member] | Derivative Liabilities [Member] | Other Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		20		18
Counterparty And Cash Collateral Netting [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		0		(1)
Fair value financial liabilities measured on recurring basis		$ 0		(32)
Counterparty And Cash Collateral Netting [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis				(1)
Counterparty And Cash Collateral Netting [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				$ (32)

[1] Investment was measured at fair value by applying the net asset value per share practical expedient, and was not classified in the fair value hierarchy in accordance with ASC 820-10. The fair value amount presented was provided to permit reconciliation of the fair value of assets categorized within the fair value hierarchy to the amounts presented in the statement of financial position.

[2] 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.