Guarantor and Non-Guarantor Financial Statements - Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Dec. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Net cash from (used in) operating activities			$ 114.2	$ 85.7
Cash flows from investing activities:
Additions to loans			(233.9)	(476.4)
Collections of loans			15.3	95.9
Net proceeds from sale of real estate			523.4	16.3
Proceeds from settlement of foreign forward contracts			36.2	7.5
Purchases of foreign currency options			(5.2)	(2.2)
Purchases of and additions to real estate			(1,534.0)	(1,538.2)
Proceeds from sale of marketable securities			6.2	0.0
Distributions from unconsolidated investments			92.0	99.3
Contributions to unconsolidated investments			(155.2)	(139.6)
Investment in marketable securities			0.0	(11.5)
(Investments in) distributions from consolidated subsidiaries, net			0.0	0.0
Net cash used in investing activities			(1,255.2)	(1,948.9)
Cash flows from financing activities:
Borrowings under line of credit			75.0	90.0
Repayment of junior subordinated debt			0.0	(40.0)
Repayment of line of credit			(200.0)	(90.0)
Borrowings under investment debt			1,632.2	825.1
Repayment of investment debt			(620.2)	(32.2)
Borrowings under senior notes payable			0.0	297.2
Debt issue costs			(15.0)	(28.5)
Issuance of common stock			215.0	190.6
Repurchase of common stock			(11.4)	(2.9)
Dividends paid			(37.7)	(28.4)
Proceeds from the issuance of KWE shares, net			0.0	1,351.1
Change in restricted cash			0.0	(42.6)
Acquisition of KWE shares from noncontrolling interest holders			(59.5)	(16.8)
Contributions from noncontrolling interests, excluding KWE			6.5	12.9
Distributions to noncontrolling interests			(205.8)	(24.3)
Net cash provided by financing activities			779.1	2,461.2
Effect of currency exchange rate changes on cash and cash equivalents			(34.2)	10.8
Net change in cash and cash equivalents	[1]		(396.1)	608.8
Cash and cash equivalents, beginning of period		$ 787.0	937.7	178.2
Cash and cash equivalents, end of period		937.7	541.6	787.0
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash from (used in) operating activities			4.8	(0.1)
Cash flows from investing activities:
Additions to loans			0.0	0.0
Collections of loans			0.0	0.0
Net proceeds from sale of real estate			0.0	0.0
Proceeds from settlement of foreign forward contracts			0.0	0.0
Purchases of foreign currency options			0.0	0.0
Purchases of and additions to real estate			0.0	0.0
Proceeds from sale of marketable securities			0.0
Distributions from unconsolidated investments			0.0	0.0
Contributions to unconsolidated investments			0.0	0.0
Investment in marketable securities				0.0
(Investments in) distributions from consolidated subsidiaries, net			(170.7)	(159.3)
Net cash used in investing activities			(170.7)	(159.3)
Cash flows from financing activities:
Borrowings under line of credit			0.0	0.0
Repayment of junior subordinated debt				0.0
Repayment of line of credit			0.0	0.0
Borrowings under investment debt			0.0	0.0
Repayment of investment debt			0.0	0.0
Borrowings under senior notes payable				0.0
Debt issue costs			0.0	0.0
Issuance of common stock			215.0	190.6
Repurchase of common stock			(11.4)	(2.9)
Dividends paid			(37.7)	(28.4)
Proceeds from the issuance of KWE shares, net				0.0
Change in restricted cash				0.0
Acquisition of KWE shares from noncontrolling interest holders			0.0	0.0
Contributions from noncontrolling interests, excluding KWE			0.0	0.0
Distributions to noncontrolling interests			0.0	0.0
Net cash provided by financing activities			165.9	159.3
Effect of currency exchange rate changes on cash and cash equivalents			0.0	0.0
Net change in cash and cash equivalents			0.0	(0.1)
Cash and cash equivalents, beginning of period		(0.1)	0.0	0.0
Cash and cash equivalents, end of period		0.0	0.0	(0.1)
Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash from (used in) operating activities			41.2	(25.7)
Cash flows from investing activities:
Additions to loans			(39.0)	0.0
Collections of loans			0.0	0.0
Net proceeds from sale of real estate			0.0	0.0
Proceeds from settlement of foreign forward contracts			17.9	0.0
Purchases of foreign currency options			(3.7)	0.0
Purchases of and additions to real estate			0.0	(0.6)
Proceeds from sale of marketable securities			0.0
Distributions from unconsolidated investments			0.0	0.3
Contributions to unconsolidated investments			(1.5)	(2.0)
Investment in marketable securities				0.0
(Investments in) distributions from consolidated subsidiaries, net			113.1	(198.4)
Net cash used in investing activities			86.8	(200.7)
Cash flows from financing activities:
Borrowings under line of credit			75.0	90.0
Repayment of junior subordinated debt				(40.0)
Repayment of line of credit			(200.0)	(90.0)
Borrowings under investment debt			0.0	0.0
Repayment of investment debt			0.0	0.0
Borrowings under senior notes payable				297.2
Debt issue costs			(0.7)	(7.8)
Issuance of common stock			0.0	0.0
Repurchase of common stock			0.0	0.0
Dividends paid			0.0	0.0
Proceeds from the issuance of KWE shares, net				0.0
Change in restricted cash				0.0
Acquisition of KWE shares from noncontrolling interest holders			0.0	0.0
Contributions from noncontrolling interests, excluding KWE			0.0	0.0
Distributions to noncontrolling interests			0.0	0.0
Net cash provided by financing activities			(125.7)	249.4
Effect of currency exchange rate changes on cash and cash equivalents			0.0	0.0
Net change in cash and cash equivalents			2.3	23.0
Cash and cash equivalents, beginning of period		71.2	38.2	48.2
Cash and cash equivalents, end of period		38.2	40.5	71.2
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash from (used in) operating activities			103.9	73.7
Cash flows from investing activities:
Additions to loans			0.0	(5.8)
Collections of loans			8.7	15.1
Net proceeds from sale of real estate			0.0	0.0
Proceeds from settlement of foreign forward contracts			0.0	0.0
Purchases of foreign currency options			0.0	0.0
Purchases of and additions to real estate			(186.3)	(71.6)
Proceeds from sale of marketable securities			6.2
Distributions from unconsolidated investments			44.5	51.6
Contributions to unconsolidated investments			(67.4)	(47.9)
Investment in marketable securities				(11.5)
(Investments in) distributions from consolidated subsidiaries, net			18.9	(65.0)
Net cash used in investing activities			(175.4)	(135.1)
Cash flows from financing activities:
Borrowings under line of credit			0.0	0.0
Repayment of junior subordinated debt				0.0
Repayment of line of credit			0.0	0.0
Borrowings under investment debt			84.0	31.5
Repayment of investment debt			(5.1)	(0.1)
Borrowings under senior notes payable				0.0
Debt issue costs			(0.9)	(0.6)
Issuance of common stock			0.0	0.0
Repurchase of common stock			0.0	0.0
Dividends paid			0.0	0.0
Proceeds from the issuance of KWE shares, net				0.0
Change in restricted cash				0.0
Acquisition of KWE shares from noncontrolling interest holders			0.0	0.0
Contributions from noncontrolling interests, excluding KWE			0.0	0.0
Distributions to noncontrolling interests			0.0	0.0
Net cash provided by financing activities			78.0	30.8
Effect of currency exchange rate changes on cash and cash equivalents			0.0	0.0
Net change in cash and cash equivalents			6.5	(30.6)
Cash and cash equivalents, beginning of period		46.6	21.0	77.2
Cash and cash equivalents, end of period		21.0	27.5	46.6
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash from (used in) operating activities			(35.7)	37.8
Cash flows from investing activities:
Additions to loans			(194.9)	(470.6)
Collections of loans			6.6	80.8
Net proceeds from sale of real estate			523.4	16.3
Proceeds from settlement of foreign forward contracts			18.3	7.5
Purchases of foreign currency options			(1.5)	(2.2)
Purchases of and additions to real estate			(1,347.7)	(1,466.0)
Proceeds from sale of marketable securities			0.0
Distributions from unconsolidated investments			47.5	47.4
Contributions to unconsolidated investments			(86.3)	(89.7)
Investment in marketable securities				0.0
(Investments in) distributions from consolidated subsidiaries, net			38.7	422.7
Net cash used in investing activities			(995.9)	(1,453.8)
Cash flows from financing activities:
Borrowings under line of credit			0.0	0.0
Repayment of junior subordinated debt				0.0
Repayment of line of credit			0.0	0.0
Borrowings under investment debt			1,548.2	793.6
Repayment of investment debt			(615.1)	(32.1)
Borrowings under senior notes payable				0.0
Debt issue costs			(13.4)	(20.1)
Issuance of common stock			0.0	0.0
Repurchase of common stock			0.0	0.0
Dividends paid			0.0	0.0
Proceeds from the issuance of KWE shares, net				1,351.1
Change in restricted cash				(42.6)
Acquisition of KWE shares from noncontrolling interest holders			(59.5)	(16.8)
Contributions from noncontrolling interests, excluding KWE			6.5	12.9
Distributions to noncontrolling interests			(205.8)	(24.3)
Net cash provided by financing activities			660.9	2,021.7
Effect of currency exchange rate changes on cash and cash equivalents			(34.2)	10.8
Net change in cash and cash equivalents			(404.9)	616.5
Cash and cash equivalents, beginning of period		669.3	878.5	52.8
Cash and cash equivalents, end of period		$ 878.5	$ 473.6	$ 669.3

[1] See discussion of non-cash effects in notes to statement of cash flows.