Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions		Jun. 30, 2017		Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		$ 7,784		$ 7,564
Fair value financial liabilities measured on recurring basis		1,694		1,784
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		407		404
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		22		27
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		145		149
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		49		52
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		8
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		17		19
Money Market Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		394		521
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		815		916
Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Corporate Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		875		150
Medium Term Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		123		101
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		1,261		1,351
Perpetual Debt And Equity Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		38		35
Cash And Cash Equivalents [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		143		163
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		21		24
Fixed Income Funds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis	[1]	79		75
Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		4,759		4,999
Fixed Maturities [Member] | U S Treasury And Government [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,027		937
Fixed Maturities [Member] | State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,164		1,440
Fixed Maturities [Member] | Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		11		9
Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,414		1,334
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		733		868
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		51		45
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		32		43
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		49		22
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		278		301
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		9		19
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		82		66
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		207		213
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				0
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		4		20
Other Liabilities [Member] | Warrant [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis		17		33
Other Liabilities [Member] | Securities Sold Not Yet Purchased [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial liabilities measured on recurring basis				0
Fair Value Inputs Level 1 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,591		1,559
Fair value financial liabilities measured on recurring basis		0		0
Fair Value Inputs Level 1 [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		0
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		394		521
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		29		26
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		143		163
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		21		24
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		1,004		825
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		916		825
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				0
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		88
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				0
Fair Value Inputs Level 2 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		3,992		4,378
Fair value financial liabilities measured on recurring basis		996		1,123
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		22		27
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		145		149
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		46		52
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		7
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		17		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		770		875
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		9
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		3,743		4,113
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		111		112
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		1,164		1,440
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		11		9
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		1,326		1,332
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		733		868
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		51		45
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		25		43
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		49		7
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		273		257
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		3
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		2
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		207		213
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				0
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		17		33
Fair Value Inputs Level 3 [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		2,122		1,552
Fair value financial liabilities measured on recurring basis		698		661
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		407		404
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]	0		0
Fair Value Inputs Level 3 [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	[2]	3
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]	0		1
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		815		916
Fair Value Inputs Level 3 [Member] | Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Corporate Loans Receivable [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		875	[2]	150
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]	123		101
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		491		476
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		12		61
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]	0		0
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]			0
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]	0		2
Fair Value Inputs Level 3 [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	[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]	0		15
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]	5		44
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]	9		19
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		80		64
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		4		20
Counterparty And Cash Collateral Netting [Member]
Accounts Notes And Loans Receivable [Line Items]
Fair value financial assets measured on recurring basis		0		0
Fair value financial liabilities measured on recurring basis		$ 0		0
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				0
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				$ 0

[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.