SEGMENT INFORMATION - Segment Information, by Segment (Details) ft² in Millions, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019 USD ($) ft² office	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) ft² segment line_of_business office	Dec. 31, 2018 USD ($)	Dec. 31, 2017 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		$ 142.3	$ 143.0	$ 143.7	$ 140.7	$ 178.7	$ 185.8	$ 218.3	$ 190.7	$ 569.7	$ 772.4	$ 801.8
General and administrative										42.4	50.8	42.2
Depreciation and amortization										187.6	206.1	212.5
Total expenses		155.0	147.9	143.8	153.1	187.8	177.2	212.5	188.9	599.8	766.4	770.8
Income from unconsolidated investments, net of depreciation and amortization		177.9	34.5	162.2	18.0	66.3	11.2	190.9	(5.4)	179.7	78.7	77.8
Gain on sale of real estate, net										434.4	371.8	226.7
Gain on sale of business										0.0	40.4	0.0
Acquisition-related expenses										(6.8)	(1.7)	(4.4)
Interest expense										(215.1)	(238.2)	(217.7)
Other income										0.4	13.1	8.3
Benefit from (provision for) income taxes		(6.3)	(10.2)	(20.9)	(4.0)	(24.3)	(6.9)	(29.4)	2.6	(41.4)	(58.0)	16.3
Net income		158.9	19.4	141.2	1.6	32.9	12.9	167.3	(1.0)	321.1	212.1	138.0
Net income attributable to the noncontrolling interests		1.6	1.3	(90.4)	(6.9)	(2.2)	(0.8)	(57.7)	(1.4)	(94.4)	(62.1)	(37.5)
Preferred dividends and accretion of preferred stock issuance costs		(2.6)	0.0	0.0	0.0					(2.6)	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		157.9	$ 20.7	$ 50.8	$ (5.3)	30.7	$ 12.1	$ 109.6	$ (2.4)	224.1	150.0	100.5
Segment Reporting Information, Assets [Abstract]
Assets	[1]	$ 7,304.5				7,381.8				7,304.5	7,381.8
Expenditures for long lived assets										$ (210.9)	(355.8)	(567.6)
Investments Segment [Member]
Segment Reporting Information [Line Items]
Average ownership interest in investments		61.00%								61.00%
Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information [Line Items]
Area of real estate property (in sq ft) | ft²		49								49
Number of offices | office		14								14
Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										$ 529.0	727.1	758.9
General and administrative										27.6	31.6	26.0
Depreciation and amortization										187.6	205.8	212.2
Total expenses										501.6	645.7	646.6
Income from unconsolidated investments, net of depreciation and amortization										143.4	51.3	66.4
Gain on sale of real estate, net										434.4	371.8	226.7
Gain on sale of business											0.0
Acquisition-related expenses										(6.8)	(1.7)	(4.4)
Interest expense										(145.6)	(161.0)	(145.6)
Other income										2.8	1.8	(5.1)
Benefit from (provision for) income taxes										(14.5)	(14.0)	(4.8)
Net income										441.1	329.6	245.5
Net income attributable to the noncontrolling interests										(94.4)	(62.1)	(37.5)
Preferred dividends and accretion of preferred stock issuance costs										0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										346.7	267.5	208.0
Segment Reporting Information, Assets [Abstract]
Assets		$ 6,945.1				7,155.0				6,945.1	7,155.0
Expenditures for long lived assets										(210.9)	(355.8)	(567.6)
Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										40.7	45.3	42.9
General and administrative										7.8	12.1	11.3
Depreciation and amortization										0.0	0.3	0.3
Total expenses										34.5	51.8	54.0
Income from unconsolidated investments, net of depreciation and amortization										36.3	27.4	11.4
Gain on sale of real estate, net										0.0	0.0	0.0
Gain on sale of business											40.4
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
Benefit from (provision for) income taxes										0.0	0.0	0.0
Net income										42.5	61.3	0.3
Net income attributable to the noncontrolling interests										0.0	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										42.5	61.3	0.3
Segment Reporting Information, Assets [Abstract]
Assets		61.1				64.3				61.1	64.3
Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										0.0	0.0	0.0
General and administrative										7.0	7.1	4.9
Depreciation and amortization										0.0	0.0	0.0
Total expenses										63.7	68.9	70.2
Income from unconsolidated investments, net of depreciation and amortization										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
Acquisition-related expenses										0.0	0.0	0.0
Interest expense										(69.5)	(77.2)	(72.1)
Other income										(2.4)	11.3	13.4
Benefit from (provision for) income taxes										(26.9)	(44.0)	21.1
Net income										(162.5)	(178.8)	(107.8)
Net income attributable to the noncontrolling interests										0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs										(2.6)
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders										(165.1)	(178.8)	(107.8)
Segment Reporting Information, Assets [Abstract]
Assets		$ 298.3				$ 162.5				298.3	162.5
Rental [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										447.4	514.6	504.7
Cost of goods sold										152.9	160.8	151.2
Rental [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										447.4	514.6	504.7
Cost of goods sold										152.9	160.8	151.2
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 of goods 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 of goods sold										0.0	0.0	0.0
Hotel [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										80.5	155.7	127.5
Cost of goods sold										60.1	121.5	100.3
Hotel [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										80.5	155.7	127.5
Cost of goods sold										60.1	121.5	100.3
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 of goods 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 of goods sold										0.0	0.0	0.0
Sale of real estate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										1.1	56.8	111.5
Cost of goods sold										1.2	52.5	80.2
Sale of real estate [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue										1.1	56.8	111.5
Cost of goods sold										1.2	52.5	80.2
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 of goods 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 of goods 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										40.7	45.3	42.9
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										40.7	45.3	42.9
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										0.0	0.0	15.2
Loan purchases, loan originations, and other [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue												15.2
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
Loan purchases, loan originations, and other [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Total revenue												0.0
Commission and marketing [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										3.8	5.9	7.2
Commission and marketing [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods 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 of goods sold										3.8	5.9	7.2
Commission and marketing [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										0.0	0.0	0.0
Compensation and related [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										151.8	168.8	177.2
Compensation and related [Member] | Operating Segments [Member] | Investments Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										72.2	73.5	76.7
Compensation and related [Member] | Operating Segments [Member] | Investment Management and Real Estate Services Segment [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										22.9	33.5	35.2
Compensation and related [Member] | Corporate [Member]
Segment Reporting Information, Income and Expense Activity [Abstract]
Cost of goods sold										$ 56.7	$ 61.8	$ 65.3

[1] The assets and liabilities as of December 31, 2019 include $267.5 million (including cash held by consolidated investments of $10.3 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $243.5 million) and $219.7 million (including investment debt of $206.0 million), respectively, from consolidated variable interest entities ("VIEs"). 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 VIEs. These assets can only be used to settle obligations of the consolidated VIEs, and the liabilities do not have recourse to the Company.