Guarantor and Non-Guarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		$ (36.6)	$ (25.1)
Cash flows from investing activities:
Issuance of loans		(6.3)	(0.4)
Proceeds from collection of loans		33.0	0.0
Additions to non refundable escrow deposits		0.0	(5.0)
Net proceeds from sale of consolidated real estate		182.0	177.3
Capital expenditures to real estate		(37.5)	(56.9)
Distributions from unconsolidated investments		79.3	5.6
Contributions to unconsolidated investments		(45.3)	(20.3)
Additions to development project asset		0.0	(1.2)
Proceeds from development project asset		2.3	1.7
Proceeds from settlement of foreign derivative contracts		32.5	0.0
Distributions from (investments in) consolidated subsidiaries, net		0.0	0.0
Net cash provided by investing activities		240.0	100.8
Cash flows from financing activities:
Borrowings under mortgage debt		22.7	296.9
Repayment of mortgage debt		(51.6)	(251.4)
Payment of debt issue costs		(4.3)	(2.1)
Repurchase and retirement of common stock		(25.6)	(7.9)
Common dividends paid		31.6	30.3
Preferred dividends paid		(3.3)	0.0
Issuance (repayment) of shareholder loans to noncontrolling interests		0.3	(10.7)
Contributions from noncontrolling interests		0.3	5.3
Distributions to noncontrolling interests		(0.2)	(122.7)
Net cash used in financing activities		(93.3)	(122.9)
Effect of currency exchange rate changes on cash and cash equivalents		(18.4)	2.1
Net change in cash and cash equivalents	[1]	91.7	(45.1)
Cash and cash equivalents, beginning of period		573.9	488.0
Cash and cash equivalents, end of period		665.6	442.9
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		(0.1)	0.2
Cash flows from investing activities:
Issuance of loans		0.0	0.0
Proceeds from collection of loans		0.0
Additions to non refundable escrow deposits			0.0
Net proceeds from sale of consolidated real estate		0.0	0.0
Capital expenditures to real estate		0.0	0.0
Distributions from unconsolidated investments		0.0	0.0
Contributions to unconsolidated investments		0.0	0.0
Additions to development project asset			0.0
Proceeds from development project asset		0.0	0.0
Proceeds from settlement of foreign derivative contracts		0.0
Distributions from (investments in) consolidated subsidiaries, net		29.8	38.0
Net cash provided by investing activities		29.8	38.0
Cash flows from financing activities:
Borrowings under mortgage debt		0.0	0.0
Repayment of mortgage debt		0.0	0.0
Payment of debt issue costs		0.0	0.0
Repurchase and retirement of common stock		(25.6)	(7.9)
Common dividends paid		31.6	30.3
Preferred dividends paid		(3.3)
Issuance (repayment) of shareholder loans to noncontrolling interests		0.0	0.0
Contributions from noncontrolling interests		0.0	0.0
Distributions to noncontrolling interests		0.0	0.0
Net cash used in financing activities		(60.5)	(38.2)
Effect of currency exchange rate changes on cash and cash equivalents		0.0	0.0
Net change in cash and cash equivalents	[1]	(30.8)	0.0
Cash and cash equivalents, beginning of period		30.8	0.0
Cash and cash equivalents, end of period		0.0	0.0
Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		(70.3)	(61.6)
Cash flows from investing activities:
Issuance of loans		(6.3)	0.0
Proceeds from collection of loans		0.0
Additions to non refundable escrow deposits			(5.0)
Net proceeds from sale of consolidated real estate		0.0	0.0
Capital expenditures to real estate		0.0	0.0
Distributions from unconsolidated investments		4.0	0.8
Contributions to unconsolidated investments		(0.1)	(0.4)
Additions to development project asset			0.0
Proceeds from development project asset		0.0	0.0
Proceeds from settlement of foreign derivative contracts		0.0
Distributions from (investments in) consolidated subsidiaries, net		116.4	100.4
Net cash provided by investing activities		114.0	95.8
Cash flows from financing activities:
Borrowings under mortgage debt		0.0	0.0
Repayment of mortgage debt		0.0	0.0
Payment of debt issue costs		(4.3)	0.0
Repurchase and retirement of common stock		0.0	0.0
Common dividends paid		0.0	0.0
Preferred dividends paid		0.0
Issuance (repayment) of shareholder loans to noncontrolling interests		0.0	0.0
Contributions from noncontrolling interests		0.0	0.0
Distributions to noncontrolling interests		0.0	0.0
Net cash used in financing activities		(4.3)	0.0
Effect of currency exchange rate changes on cash and cash equivalents		0.0	0.0
Net change in cash and cash equivalents	[1]	39.4	34.2
Cash and cash equivalents, beginning of period		6.4	1.9
Cash and cash equivalents, end of period		45.8	36.1
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		(13.8)	(1.4)
Cash flows from investing activities:
Issuance of loans		0.0	(0.4)
Proceeds from collection of loans		0.0
Additions to non refundable escrow deposits			0.0
Net proceeds from sale of consolidated real estate		0.0	0.0
Capital expenditures to real estate		(17.3)	(10.3)
Distributions from unconsolidated investments		31.4	1.7
Contributions to unconsolidated investments		(13.7)	(14.2)
Additions to development project asset			0.0
Proceeds from development project asset		0.0	0.0
Proceeds from settlement of foreign derivative contracts		32.5
Distributions from (investments in) consolidated subsidiaries, net		13.0	40.0
Net cash provided by investing activities		45.9	16.8
Cash flows from financing activities:
Borrowings under mortgage debt		6.7	0.0
Repayment of mortgage debt		(50.1)	(0.3)
Payment of debt issue costs		0.0	0.0
Repurchase and retirement of common stock		0.0	0.0
Common dividends paid		0.0	0.0
Preferred dividends paid		0.0
Issuance (repayment) of shareholder loans to noncontrolling interests		0.0	0.0
Contributions from noncontrolling interests		0.0	0.0
Distributions to noncontrolling interests		0.0	0.0
Net cash used in financing activities		(43.4)	(0.3)
Effect of currency exchange rate changes on cash and cash equivalents		0.0	0.0
Net change in cash and cash equivalents		(11.3)	15.1
Cash and cash equivalents, beginning of period		102.7	101.9
Cash and cash equivalents, end of period		91.4	117.0
Non-guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		47.6	37.7
Cash flows from investing activities:
Issuance of loans		0.0	0.0
Proceeds from collection of loans		33.0
Additions to non refundable escrow deposits			0.0
Net proceeds from sale of consolidated real estate		182.0	177.3
Capital expenditures to real estate		(20.2)	(46.6)
Distributions from unconsolidated investments		43.9	3.1
Contributions to unconsolidated investments		(31.5)	(5.7)
Additions to development project asset			(1.2)
Proceeds from development project asset		2.3	1.7
Proceeds from settlement of foreign derivative contracts		0.0
Distributions from (investments in) consolidated subsidiaries, net		(159.2)	(178.4)
Net cash provided by investing activities		50.3	(49.8)
Cash flows from financing activities:
Borrowings under mortgage debt		16.0	296.9
Repayment of mortgage debt		(1.5)	(251.1)
Payment of debt issue costs		0.0	(2.1)
Repurchase and retirement of common stock		0.0	0.0
Common dividends paid		0.0	0.0
Preferred dividends paid		0.0
Issuance (repayment) of shareholder loans to noncontrolling interests		0.3	(10.7)
Contributions from noncontrolling interests		0.3	5.3
Distributions to noncontrolling interests		(0.2)	(122.7)
Net cash used in financing activities		14.9	(84.4)
Effect of currency exchange rate changes on cash and cash equivalents		(18.4)	2.1
Net change in cash and cash equivalents	[1]	94.4	(94.4)
Cash and cash equivalents, beginning of period		434.0	384.2
Cash and cash equivalents, end of period		$ 528.4	$ 289.8

[1] See discussion of non-cash effects in the supplemental cash flow information.