SEGMENT INFORMATION - Segment Information, by Segment (Details) ft² in Millions, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018 USD ($) ft² office	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) ft² segment office line_of_business	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment										2
Number of main lines of businesses | line_of_business										5
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue		$ 178.7	$ 185.8	$ 218.3	$ 190.7	$ 181.3	$ 272.5	$ 180.4	$ 167.6	$ 773.5	$ 801.8	$ 690.4
General and administrative										50.8	42.2	45.4
Depreciation and amortization										206.1	212.5	198.2
Total expenses		187.8	177.2	212.5	188.9	206.0	231.2	178.3	155.3	766.4	770.8	691.9
Income from unconsolidated investments		66.3	11.2	190.9	(5.4)	112.9	(35.2)	28.5	(15.5)	78.7	77.8	139.6
Gain on sale of real estate, net										371.8	226.7	130.7
Gain on sale of business										40.4	0.0	0.0
Acquisition-related gains										0.0	0.0	16.2
Acquisition-related expenses										(1.7)	(4.4)	(9.5)
Interest expense										(238.2)	(217.7)	(191.6)
Other income										12.0	8.3	6.6
(Provision for) benefit from income taxes		(24.3)	(6.9)	(29.4)	2.6	17.2	3.7	(8.8)	4.2	(58.0)	16.3	(14.0)
Net income		32.9	12.9	167.3	(1.0)	105.4	9.8	21.8	1.0	212.1	138.0	76.5
Net income attributable to the noncontrolling interests		(2.2)	(0.8)	(57.7)	(1.4)	(6.2)	(18.7)	(12.4)	(0.2)	(62.1)	(37.5)	(70.9)
Preferred dividends and accretion of preferred stock issuance costs										0.0	0.0	(2.8)
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		30.7	$ 12.1	$ 109.6	$ (2.4)	99.2	$ (8.9)	$ 9.4	$ 0.8	150.0	100.5	2.8
Segment Reporting Information, Assets [Abstract]
Assets	[1]	$ 7,357.1				7,724.8				7,357.1	7,724.8
Expenditures for long lived assets										$ (571.8)	(814.3)	(949.6)
Investments Segment [Member]
Segment Reporting Information [Line Items]
Average ownership interest in investments		63.00%								63.00%
Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information [Line Items]
Area of real estate property (in sq ft) | ft²		53								53
Number of offices | office		17								17
Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										$ 728.2	758.9	644.0
General and administrative										31.6	26.0	26.5
Depreciation and amortization										205.8	212.2	197.4
Total expenses										645.7	646.6	540.0
Income from unconsolidated investments										51.3	66.4	122.8
Gain on sale of real estate, net										371.8	226.7	130.7
Gain on sale of business										0.0	0.0	0.0
Acquisition-related gains												16.2
Acquisition-related expenses										(1.7)	(4.4)	(9.5)
Interest expense										(161.0)	(145.6)	(137.4)
Other income										0.7	(5.1)	(1.2)
(Provision for) benefit from income taxes										(14.0)	(4.8)	5.0
Net income										329.6	245.5	230.6
Net income attributable to the noncontrolling interests										(62.1)	(37.5)	(70.9)
Preferred dividends and accretion of preferred stock issuance costs												0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										267.5	208.0	159.7
Segment Reporting Information, Assets [Abstract]
Assets		$ 7,155.0				7,563.7				7,155.0	7,563.7
Expenditures for long lived assets										(571.8)	(814.3)	(949.6)
Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										45.3	42.9	46.4
General and administrative										12.1	11.3	13.3
Depreciation and amortization										0.3	0.3	0.8
Total expenses										51.8	54.0	58.3
Income from unconsolidated investments										27.4	11.4	16.8
Gain on sale of real estate, net										0.0	0.0	0.0
Gain on sale of business										40.4	0.0	0.0
Acquisition-related gains												0.0
Acquisition-related expenses										0.0	0.0	0.0
Interest expense										0.0	0.0	0.0
Other income										0.0	0.0	0.0
(Provision for) benefit from income taxes										0.0	0.0	0.0
Net income										61.3	0.3	4.9
Net income attributable to the noncontrolling interests										0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs												0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										61.3	0.3	4.9
Segment Reporting Information, Assets [Abstract]
Assets		64.3				70.5				64.3	70.5
Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
General and administrative										7.1	4.9	5.6
Depreciation and amortization										0.0	0.0	0.0
Total expenses										68.9	70.2	93.6
Income from unconsolidated investments										0.0	0.0	0.0
Gain on sale of real estate, net										0.0	0.0	0.0
Gain on sale of business										0.0	0.0	0.0
Acquisition-related gains												0.0
Acquisition-related expenses										0.0	0.0	(54.2)
Interest expense										(77.2)	(72.1)
Other income										11.3	13.4	7.8
(Provision for) benefit from income taxes										(44.0)	21.1	(19.0)
Net income										(178.8)	(107.8)	(159.0)
Net income attributable to the noncontrolling interests										0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs												(2.8)
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										(178.8)	(107.8)	(161.8)
Segment Reporting Information, Assets [Abstract]
Assets		$ 137.8				$ 90.6				137.8	90.6
Rental [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										514.6	504.7	485.9
Cost goods and services sold										160.8	151.2	135.4
Rental [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										514.6	504.7	485.9
Cost goods and services sold										160.8	151.2	135.4
Rental [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Rental [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Hotel [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										155.7	127.5	116.2
Cost goods and services sold										121.5	100.3	96.3
Hotel [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										155.7	127.5	116.2
Cost goods and services sold										121.5	100.3	96.3
Hotel [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Hotel [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Sale of real estate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										56.8	111.5	29.3
Cost goods and services sold										52.5	80.2	22.1
Sale of real estate [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										56.8	111.5	29.3
Cost goods and services sold										52.5	80.2	22.1
Sale of real estate [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Sale of real estate [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Cost goods and services sold										0.0	0.0	0.0
Investment management, property services and research fees [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										45.3	42.9	46.4
Investment management, property services and research fees [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Investment management, property services and research fees [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										45.3	42.9	46.4
Investment management, property services and research fees [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Loan purchases, loan originations, and other [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										1.1	15.2	12.6
Loan purchases, loan originations, and other [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										1.1	15.2	12.6
Loan purchases, loan originations, and other [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Loan purchases, loan originations, and other [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
Commission and marketing [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										5.9	7.2	8.0
Commission and marketing [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										0.0	0.0	0.0
Commission and marketing [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										5.9	7.2	8.0
Commission and marketing [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										0.0	0.0	0.0
Compensation and related [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										168.8	177.2	186.5
Compensation and related [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										73.5	76.7	62.3
Compensation and related [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										33.5	35.2	36.2
Compensation and related [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost goods and services sold										$ 61.8	$ 65.3	$ 88.0

[1] The assets and liabilities as of December 31, 2018 include $657.8 million (including cash held by consolidated investments of $31.6 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $602.5 million) and $317.4 million (including investment debt of $283.6 million), respectively, from consolidated variable interest entities ("VIEs"). The assets and liabilities as of December 31, 2017 include $904.4 million (including cash held by consolidated investments of $39.1 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $789.1 million) and $510.0 million (including investment debt of $475.3 million), respectively, from VIEs. These assets can only be used to settle obligations of the consolidated VIEs, and the liabilities do not have recourse to the Company.