Segment Information (Details) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) segment
Segment Reporting Information [Line Items]
Number of operating segments | segment		2		2
Revenue
Total revenue		$ 123.3	$ 140.7
Expenses
General and administrative		9.5	10.9
Depreciation and amortization		45.5	49.1
Total expenses		129.8	153.1
Non-operating income (expense)
Income from unconsolidated investments		10.9	41.7
Transaction-related expenses		44.2	34.9
Transaction-related expenses		(0.2)	(0.8)
Interest expense		(48.8)	(55.3)
Other income (loss)		0.2	(2.5)
Provision for income taxes		(5.7)	(4.0)
Net (loss) income		(5.9)	1.6
Net income attributable to the noncontrolling interests		0.3	(6.9)
Preferred dividends and accretion of preferred stock issuance costs		(4.3)	0.0
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		(9.9)	(5.3)
Segment Reporting Information, Assets [Abstract]
Total assets	[1]	6,948.0		$ 7,304.5
Unconsolidated investments		1,256.4		1,334.6
Corporate, Non-Segment [Member]
Revenue
Total revenue		3.9	3.7
Expenses
General and administrative		2.2	2.6
Depreciation and amortization		0.0	0.0
Total expenses		17.8	21.3
Non-operating income (expense)
Income from unconsolidated investments		0.0	0.0
Transaction-related expenses		0.0	0.0
Transaction-related expenses		0.0	0.0
Interest expense		(15.4)	(18.2)
Other income (loss)		0.9	0.3
Provision for income taxes		(0.6)	(1.9)
Net (loss) income		(29.0)	(37.4)
Net income attributable to the noncontrolling interests		0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs		(4.3)	0.0
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		(33.3)	(37.4)
Segment Reporting Information, Assets [Abstract]
Total assets		317.8		298.3
Rental [Member]
Revenue
Total revenue		107.7	115.8
Expenses
Cost of goods and services		36.7	41.0
Rental [Member] | Corporate, Non-Segment [Member]
Revenue
Total revenue		0.0	0.0
Expenses
Cost of goods and services		0.0	0.0
Hotel [Member]
Revenue
Total revenue		7.2	15.0
Expenses
Cost of goods and services		6.0	14.6
Hotel [Member] | Corporate, Non-Segment [Member]
Revenue
Total revenue		0.0	0.0
Expenses
Cost of goods and services		0.0	0.0
Sale of Real Estate [Member]
Revenue
Total revenue		0.0	1.1
Expenses
Cost of goods and services		0.0	1.2
Sale of Real Estate [Member] | Corporate, Non-Segment [Member]
Revenue
Total revenue			0.0
Expenses
Cost of goods and services			0.0
Investment Management and Property Services Fees [Member]
Revenue
Total revenue		8.4	8.8
Investment Management and Property Services Fees [Member] | Corporate, Non-Segment [Member]
Revenue
Total revenue		3.9	3.7
Commission and Marketing [Member]
Expenses
Cost of goods and services		0.7	1.0
Commission and Marketing [Member] | Corporate, Non-Segment [Member]
Expenses
Cost of goods and services		0.7	1.0
Compensation and Related [Member]
Expenses
Cost of goods and services		31.4	35.3
Compensation and Related [Member] | Corporate, Non-Segment [Member]
Expenses
Cost of goods and services		14.9	17.7
Consolidated [Member] | Operating Segments [Member]
Revenue
Total revenue		114.9	131.9
Expenses
General and administrative		5.6	5.8
Depreciation and amortization		45.5	49.1
Total expenses		105.7	122.9
Non-operating income (expense)
Income from unconsolidated investments		0.0	0.0
Transaction-related expenses		44.2	34.9
Transaction-related expenses		(0.2)	(0.8)
Interest expense		(33.4)	(37.1)
Other income (loss)		(0.7)	(2.8)
Provision for income taxes		(5.1)	(2.1)
Net (loss) income		14.0	1.1
Net income attributable to the noncontrolling interests		0.3	(6.9)
Preferred dividends and accretion of preferred stock issuance costs		0.0	0.0
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		14.3	(5.8)
Segment Reporting Information, Assets [Abstract]
Total assets		5,373.8		5,671.6
Consolidated [Member] | Rental [Member] | Operating Segments [Member]
Revenue
Total revenue		107.7	115.8
Expenses
Cost of goods and services		36.7	41.0
Consolidated [Member] | Hotel [Member] | Operating Segments [Member]
Revenue
Total revenue		7.2	15.0
Expenses
Cost of goods and services		6.0	14.6
Consolidated [Member] | Sale of Real Estate [Member] | Operating Segments [Member]
Revenue
Total revenue			1.1
Expenses
Cost of goods and services			1.2
Consolidated [Member] | Investment Management and Property Services Fees [Member] | Operating Segments [Member]
Revenue
Total revenue		0.0	0.0
Consolidated [Member] | Commission and Marketing [Member] | Operating Segments [Member]
Expenses
Cost of goods and services		0.0	0.0
Consolidated [Member] | Compensation and Related [Member] | Operating Segments [Member]
Expenses
Cost of goods and services		11.9	11.2
Co-Investments [Member] | Operating Segments [Member]
Revenue
Total revenue		4.5	5.1
Expenses
General and administrative		1.7	2.5
Depreciation and amortization		0.0	0.0
Total expenses		6.3	8.9
Non-operating income (expense)
Income from unconsolidated investments		10.9	41.7
Transaction-related expenses		0.0	0.0
Transaction-related expenses		0.0	0.0
Interest expense		0.0	0.0
Other income (loss)		0.0	0.0
Provision for income taxes		0.0	0.0
Net (loss) income		9.1	37.9
Net income attributable to the noncontrolling interests		0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs		0.0	0.0
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		9.1	37.9
Segment Reporting Information, Assets [Abstract]
Unconsolidated investments		1,256.4		$ 1,334.6
Co-Investments [Member] | Rental [Member] | Operating Segments [Member]
Revenue
Total revenue		0.0	0.0
Expenses
Cost of goods and services		0.0	0.0
Co-Investments [Member] | Hotel [Member] | Operating Segments [Member]
Revenue
Total revenue		0.0	0.0
Expenses
Cost of goods and services		0.0	0.0
Co-Investments [Member] | Sale of Real Estate [Member] | Operating Segments [Member]
Revenue
Total revenue			0.0
Expenses
Cost of goods and services			0.0
Co-Investments [Member] | Investment Management and Property Services Fees [Member] | Operating Segments [Member]
Revenue
Total revenue		4.5	5.1
Co-Investments [Member] | Commission and Marketing [Member] | Operating Segments [Member]
Expenses
Cost of goods and services		0.0	0.0
Co-Investments [Member] | Compensation and Related [Member] | Operating Segments [Member]
Expenses
Cost of goods and services		$ 4.6	$ 6.4
Minimum [Member]
Segment Reporting Information [Line Items]
Average ownership interest in investments		5.00%
Maximum [Member]
Segment Reporting Information [Line Items]
Average ownership interest in investments		50.00%

[1] The assets and liabilities as of March 31, 2020 include $136.3 million (including cash held by consolidated investments of $4.5 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $122.9 million) and $84.4 million (including investment debt of $78.6 million), respectively, from consolidated variable interest entities ("VIEs"). 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 VIEs. These assets can only be used to settle obligations of the consolidated VIEs, and the liabilities do not have recourse to the Company.