Summary of Significant Accounting Policies (Details 3)	9 Months Ended
Sep. 30, 2011 month grade day approach issuer component
Consolidation
Minimum percentage of voting interest required to consolidate non-VIEs (as a percent)	50.00%
Fair Value of Financial Instruments
Number of approaches used to determine fair value of investments	2
Cash and Cash Equivalents
Maximum term of original maturity to classify instrument as cash equivalents (in months)	3
Corporate Loans
Period for determination of non-accrual status (in days)	90
Allowance for Loan Losses
Number of components in the loans receivable allowance for loan losses	2
Number of internally assigned risk grades	3
Income Taxes
Minimum percentage of likelihood a tax benefit will be realized to record the tax impact (as a percent)	50.00%

Represents the period for determination of non-accrual status of corporate loans.

Name:	kfn_CorporateLoansDelinquentPeriodForNonaccrualStatus
Namespace Prefix:	kfn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Name:	kfn_FairValueOfFinancialInstrumentsAbstract
Namespace Prefix:	kfn
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The number of components in the loans receivable allowance for loan losses.

Name:	kfn_LoansReceivableAllowanceForLoanLossesNumberOfComponents
Namespace Prefix:	kfn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the maximum original term of maturity for an instrument to be classified as cash or cash equivalent.

Name:	kfn_MaximumTermOfOriginalMaturityToClassifyAnInstrumentAsCashEquivalents
Namespace Prefix:	kfn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the minimum percentage of likelihood that a tax benefit will be realized in order to record the tax impact.

Name:	kfn_MinimumPercentageRequiredToRecognizeTaxBenefit
Namespace Prefix:	kfn
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The minimum percentage of voting interest required to consolidate non-Variable Interest Entities

Name:	kfn_MinimumPercentVotingInterestInEntityOtherThanVariableInterestEntityForConsolidation
Namespace Prefix:	kfn
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the number of approaches used to determine the fair value of investments.

Name:	kfn_NumberOfApproachesUsedToDetermineFairValueOfInvestments
Namespace Prefix:	kfn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the number of internally assigned risk grades to determine the impairment on loans.

Name:	kfn_NumberOfInternallyAssignedRiskGrades
Namespace Prefix:	kfn
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_CashAndCashEquivalentsAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_LoansReceivableNetAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_ProvisionForLoanAndLeaseLossesAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration