GUARANTOR AND NON-GUARANTOR FINANCIAL STATEMENTS - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ (19.5)	$ 93.1	$ 73.0
Cash flows from investing activities:
Proceeds from collection of loans	0.6	5.8	16.9
Issuance of loans	(2.7)	(2.2)
Nonrefundable escrow deposits	0.0	(5.0)	0.0
Net proceeds from sale of consolidated real estate	701.0	1,386.1	659.1
Net proceeds from sale of a business		43.4
Purchases of consolidated real estate	(210.9)	(355.8)	(567.6)
Capital expenditures to real estate	(191.1)	(216.0)	(246.7)
Investment in marketable securities		(0.2)	(0.8)
Proceeds from sale of marketable securities	0.0	7.4	1.1
Investing distributions from unconsolidated investments	115.0	63.7	133.4
Contributions to unconsolidated investments	(266.0)	(396.1)	(79.9)
Proceeds from settlement of foreign currency derivative contracts	33.4	10.7	(2.8)
Purchases of foreign currency derivative contracts	0.0	(0.6)	(0.4)
Additions to development project asset	(1.2)	(29.1)	(19.4)
Proceeds from development project asset	4.2	81.0	36.9
(Investments in) distributions from consolidated subsidiaries, net	0.0	0.0	0.0
Net cash provided by (used in) investing activities	182.3	593.1	(70.2)
Cash flow from financing activities:
Borrowings under senior notes payable	0.0	246.6	0.0
Borrowings under line of credit/term loan	125.0	225.0	800.0
Repayment of senior notes payable	0.0	0.0	(55.0)
Repayment of line of credit/term loan	(200.0)	(450.0)	(500.0)
Borrowings under mortgage debt	488.6	725.0	848.3
Borrowings under investment debt	488.6	725.0	848.3
Repayment of investment debt	(391.4)	(866.8)	(684.7)
Payment of loan fees	(4.8)	(9.5)	(9.5)
Repayment of shareholder loans to noncontrolling interests	(11.2)	0.0	0.0
Repurchase of common stock	(20.7)	(177.9)	(67.7)
Issuance of preferred stock	295.2	0.0	0.0
Common stock dividends paid	(114.9)	(111.2)	(59.2)
Preferred stock dividends paid	(2.6)	0.0	0.0
Dividends paid		(111.2)	(59.2)
KWE closing dividend		(17.2)
Costs associated with KWE Transaction			(55.8)
Cash paid to acquire noncontrolling interest in KWE	0.0	0.0	(719.8)
Acquisition of noncontrolling interests		0.0	(3.3)
Contributions from noncontrolling interests	15.0	23.2	47.4
Distributions to noncontrolling interests	(264.0)	(116.0)	(106.0)
Net cash used in financing activities	(85.8)	(528.8)	(565.3)
Effect of currency exchange rate changes on cash and cash equivalents	8.9	(20.7)	28.1
Net change in cash and cash equivalents	85.9	136.7	(534.4)
Cash and cash equivalents, beginning of year	488.0	351.3	885.7
Cash and cash equivalents, end of year	573.9	488.0	351.3
Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(3.7)	(1.2)	(15.3)
Cash flows from investing activities:
Proceeds from collection of loans	0.0	0.0	0.0
Issuance of loans	0.0	0.0
Nonrefundable escrow deposits	0.0	0.0
Net proceeds from sale of consolidated real estate	0.0	0.0	0.0
Net proceeds from sale of a business		0.0
Purchases of consolidated real estate	0.0	0.0	0.0
Capital expenditures to real estate	0.0	0.0	0.0
Investment in marketable securities		0.0	0.0
Proceeds from sale of marketable securities		0.0	0.0
Investing distributions from unconsolidated investments	0.0	0.0	0.0
Contributions to unconsolidated investments	0.0	0.0	0.0
Proceeds from settlement of foreign currency derivative contracts	0.0	0.0	0.0
Purchases of foreign currency derivative contracts	0.0	0.0	0.0
Additions to development project asset	0.0	0.0	0.0
Proceeds from development project asset	0.0	0.0	0.0
(Investments in) distributions from consolidated subsidiaries, net	(122.5)	290.3	198.0
Net cash provided by (used in) investing activities	(122.5)	290.3	198.0
Cash flow from financing activities:
Borrowings under senior notes payable	0.0	0.0
Borrowings under line of credit/term loan	0.0	0.0	0.0
Repayment of senior notes payable			0.0
Repayment of line of credit/term loan	0.0	0.0	0.0
Borrowings under mortgage debt	0.0	0.0	0.0
Borrowings under investment debt	0.0	0.0	0.0
Repayment of investment debt	0.0	0.0	0.0
Payment of loan fees	0.0	0.0	0.0
Repayment of shareholder loans to noncontrolling interests	0.0
Repurchase of common stock	(20.7)	(177.9)	(67.7)
Issuance of preferred stock	295.2
Common stock dividends paid	(114.9)
Preferred stock dividends paid	(2.6)
Dividends paid		(111.2)	(59.2)
KWE closing dividend		0.0
Costs associated with KWE Transaction			(55.8)
Cash paid to acquire noncontrolling interest in KWE			0.0
Acquisition of noncontrolling interests			0.0
Contributions from noncontrolling interests	0.0	0.0	0.0
Distributions to noncontrolling interests	0.0	0.0	0.0
Net cash used in financing activities	157.0	(289.1)	(182.7)
Effect of currency exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net change in cash and cash equivalents	30.8	0.0	0.0
Cash and cash equivalents, beginning of year	0.0	0.0	0.0
Cash and cash equivalents, end of year	30.8	0.0	0.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	(130.4)	(133.7)	(182.8)
Cash flows from investing activities:
Proceeds from collection of loans	0.0	0.0	0.0
Issuance of loans	0.0	0.0
Nonrefundable escrow deposits	0.0	(5.0)
Net proceeds from sale of consolidated real estate	0.0	0.0	0.0
Net proceeds from sale of a business		0.0
Purchases of consolidated real estate	0.0	0.0	0.0
Capital expenditures to real estate	0.0	0.0	0.0
Investment in marketable securities		(0.2)	0.0
Proceeds from sale of marketable securities		0.0	0.0
Investing distributions from unconsolidated investments	0.8	0.0	0.0
Contributions to unconsolidated investments	(1.7)	(1.2)	0.0
Proceeds from settlement of foreign currency derivative contracts	0.0	10.7	(2.8)
Purchases of foreign currency derivative contracts	0.0	(0.6)	(0.4)
Additions to development project asset	0.0	0.0	0.0
Proceeds from development project asset	0.0	0.0	0.0
(Investments in) distributions from consolidated subsidiaries, net	210.8	81.4	(126.2)
Net cash provided by (used in) investing activities	209.9	85.1	(129.4)
Cash flow from financing activities:
Borrowings under senior notes payable	0.0	246.6
Borrowings under line of credit/term loan	125.0	225.0	800.0
Repayment of senior notes payable			(55.0)
Repayment of line of credit/term loan	(200.0)	(450.0)	(500.0)
Borrowings under mortgage debt	0.0	0.0	0.0
Borrowings under investment debt	0.0	0.0	0.0
Repayment of investment debt	0.0	0.0	0.0
Payment of loan fees	0.0	(4.5)	(5.4)
Repayment of shareholder loans to noncontrolling interests	0.0
Repurchase of common stock	0.0	0.0	0.0
Issuance of preferred stock	0.0
Common stock dividends paid	0.0
Preferred stock dividends paid	0.0
Dividends paid		0.0	0.0
KWE closing dividend		0.0
Costs associated with KWE Transaction			0.0
Cash paid to acquire noncontrolling interest in KWE			0.0
Acquisition of noncontrolling interests			0.0
Contributions from noncontrolling interests	0.0	0.0	0.0
Distributions to noncontrolling interests	0.0	0.0	0.0
Net cash used in financing activities	(75.0)	17.1	239.6
Effect of currency exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net change in cash and cash equivalents	4.5	(31.5)	(72.6)
Cash and cash equivalents, beginning of year	1.9	33.4	106.0
Cash and cash equivalents, end of year	6.4	1.9	33.4
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	24.1	66.3	(51.4)
Cash flows from investing activities:
Proceeds from collection of loans	0.6	5.8	6.4
Issuance of loans	(2.3)	(0.9)
Nonrefundable escrow deposits	0.0	0.0
Net proceeds from sale of consolidated real estate	27.6	161.2	130.8
Net proceeds from sale of a business		43.4
Purchases of consolidated real estate	(97.5)	(242.3)	(421.6)
Capital expenditures to real estate	(59.8)	(27.9)	(0.9)
Investment in marketable securities		0.0	(0.8)
Proceeds from sale of marketable securities		7.4	1.1
Investing distributions from unconsolidated investments	80.6	25.9	95.2
Contributions to unconsolidated investments	(153.9)	(92.9)	(49.8)
Proceeds from settlement of foreign currency derivative contracts	33.4	0.0	0.0
Purchases of foreign currency derivative contracts	0.0	0.0	0.0
Additions to development project asset	0.0	0.0	0.0
Proceeds from development project asset	0.0	0.0	0.0
(Investments in) distributions from consolidated subsidiaries, net	160.3	55.8	166.3
Net cash provided by (used in) investing activities	(11.0)	(64.5)	(73.3)
Cash flow from financing activities:
Borrowings under senior notes payable	0.0	0.0
Borrowings under line of credit/term loan	0.0	0.0	0.0
Repayment of senior notes payable			0.0
Repayment of line of credit/term loan	0.0	0.0	0.0
Borrowings under mortgage debt	3.5	325.3	239.5
Borrowings under investment debt	3.5	325.3	239.5
Repayment of investment debt	(15.0)	(278.1)	(103.4)
Payment of loan fees	(0.8)	(2.0)	(1.9)
Repayment of shareholder loans to noncontrolling interests	0.0
Repurchase of common stock	0.0	0.0	0.0
Issuance of preferred stock	0.0
Common stock dividends paid	0.0
Preferred stock dividends paid	0.0
Dividends paid		0.0	0.0
KWE closing dividend		0.0
Costs associated with KWE Transaction			0.0
Cash paid to acquire noncontrolling interest in KWE			0.0
Acquisition of noncontrolling interests			0.0
Contributions from noncontrolling interests	0.0	0.0	0.0
Distributions to noncontrolling interests	0.0	0.0	0.0
Net cash used in financing activities	(12.3)	45.2	134.2
Effect of currency exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net change in cash and cash equivalents	0.8	47.0	9.5
Cash and cash equivalents, beginning of year	101.9	54.9	45.4
Cash and cash equivalents, end of year	102.7	101.9	54.9
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	90.5	161.7	322.5
Cash flows from investing activities:
Proceeds from collection of loans	0.0	0.0	10.5
Issuance of loans	(0.4)	(1.3)
Nonrefundable escrow deposits	0.0	0.0
Net proceeds from sale of consolidated real estate	673.4	1,224.9	528.3
Net proceeds from sale of a business		0.0
Purchases of consolidated real estate	(113.4)	(113.5)	(146.0)
Capital expenditures to real estate	(131.3)	(188.1)	(245.8)
Investment in marketable securities		0.0	0.0
Proceeds from sale of marketable securities		0.0	0.0
Investing distributions from unconsolidated investments	33.6	37.8	38.2
Contributions to unconsolidated investments	(110.4)	(302.0)	(30.1)
Proceeds from settlement of foreign currency derivative contracts	0.0	0.0	0.0
Purchases of foreign currency derivative contracts	0.0	0.0	0.0
Additions to development project asset	(1.2)	(29.1)	(19.4)
Proceeds from development project asset	4.2	81.0	36.9
(Investments in) distributions from consolidated subsidiaries, net	(248.6)	(427.5)	(238.1)
Net cash provided by (used in) investing activities	105.9	282.2	(65.5)
Cash flow from financing activities:
Borrowings under senior notes payable	0.0	0.0
Borrowings under line of credit/term loan	0.0	0.0	0.0
Repayment of senior notes payable			0.0
Repayment of line of credit/term loan	0.0	0.0	0.0
Borrowings under mortgage debt	485.1	399.7	608.8
Borrowings under investment debt	485.1	399.7	608.8
Repayment of investment debt	(376.4)	(588.7)	(581.3)
Payment of loan fees	(4.0)	(3.0)	(2.2)
Repayment of shareholder loans to noncontrolling interests	(11.2)
Repurchase of common stock	0.0	0.0	0.0
Issuance of preferred stock	0.0
Common stock dividends paid	0.0
Preferred stock dividends paid	0.0
Dividends paid		0.0	0.0
KWE closing dividend		(17.2)
Costs associated with KWE Transaction			0.0
Cash paid to acquire noncontrolling interest in KWE			(719.8)
Acquisition of noncontrolling interests			(3.3)
Contributions from noncontrolling interests	15.0	23.2	47.4
Distributions to noncontrolling interests	(264.0)	(116.0)	(106.0)
Net cash used in financing activities	(155.5)	(302.0)	(756.4)
Effect of currency exchange rate changes on cash and cash equivalents	8.9	(20.7)	28.1
Net change in cash and cash equivalents	49.8	121.2	(471.3)
Cash and cash equivalents, beginning of year	384.2	263.0	734.3
Cash and cash equivalents, end of year	$ 434.0	$ 384.2	$ 263.0