GUARANTOR AND NON-GUARANTOR FINANCIAL STATEMENTS - Consolidating Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Total revenue	$ 178.7	$ 185.8	$ 218.3	$ 190.7	$ 181.3	$ 272.5	$ 180.4	$ 167.6	$ 773.5	$ 801.8	$ 690.4
Expenses
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
Income from consolidated subsidiaries									0.0	0.0	0.0
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
Income before (provision for) benefit from income taxes	57.2	19.8	196.7	(3.6)	88.2	6.1	30.6	(3.2)	270.1	121.7	90.5
(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) loss 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
Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Expenses
General and administrative									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Total expenses									37.1	38.4	65.1
Income from unconsolidated investments									0.0	0.0	0.0
Income from consolidated subsidiaries									249.2	176.4	141.6
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	0.0	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
Income before (provision for) benefit from income taxes									212.1	138.0	76.5
(Provision for) benefit from income taxes									0.0	0.0	0.0
Net income									212.1	138.0	76.5
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
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									212.1	138.0	73.7
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.1
Expenses
General and administrative									20.3	14.0	15.9
Depreciation and amortization									1.3	1.4	1.3
Total expenses									92.9	93.7	83.6
Income from unconsolidated investments									(1.3)	3.7	5.6
Income from consolidated subsidiaries									451.3	307.5	285.1
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	0.0	0.0
Acquisition-related expenses									(0.1)	0.0	0.0
Interest expense									(77.1)	(72.1)	(54.2)
Other income									13.3	9.9	7.7
Income before (provision for) benefit from income taxes									293.2	155.3	160.7
(Provision for) benefit from income taxes									(44.0)	21.1	(19.1)
Net income									249.2	176.4	141.6
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs									0.0	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders									249.2	176.4	141.6
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									210.4	181.4	168.1
Expenses
General and administrative									21.2	17.6	16.3
Depreciation and amortization									56.9	50.1	39.5
Total expenses									201.4	184.0	168.9
Income from unconsolidated investments									60.3	41.7	76.9
Income from consolidated subsidiaries									332.7	256.2	204.9
Gain on sale of real estate, net									61.4	46.6	19.6
Gain on sale of business									40.4	0.0	0.0
Acquisition-related gains									0.0	0.0	7.6
Acquisition-related expenses									(1.1)	(1.3)	(2.3)
Interest expense									(52.8)	(38.0)	(25.4)
Other income									0.0	1.6	(2.7)
Income before (provision for) benefit from income taxes									449.9	304.2	277.8
(Provision for) benefit from income taxes									1.4	3.3	7.3
Net income									451.3	307.5	285.1
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs									0.0	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders									451.3	307.5	285.1
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									563.1	620.4	522.2
Expenses
General and administrative									9.3	10.6	13.2
Depreciation and amortization									147.9	161.0	157.4
Total expenses									435.0	454.7	374.3
Income from unconsolidated investments									19.7	32.4	57.1
Income from consolidated subsidiaries									0.0	0.0	0.0
Gain on sale of real estate, net									310.4	180.1	111.1
Gain on sale of business									0.0	0.0	0.0
Acquisition-related gains									0.0	0.0	8.6
Acquisition-related expenses									(0.5)	(3.1)	(7.2)
Interest expense									(108.3)	(107.6)	(112.0)
Other income									(1.3)	(3.2)	1.6
Income before (provision for) benefit from income taxes									348.1	264.3	207.1
(Provision for) benefit from income taxes									(15.4)	(8.1)	(2.2)
Net income									332.7	256.2	204.9
Net (income) loss attributable to the noncontrolling interests									(62.1)	(37.5)	(70.9)
Preferred dividends and accretion of preferred stock issuance costs									0.0	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders									270.6	218.7	134.0
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Expenses
General and administrative									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Total expenses									0.0	0.0	0.0
Income from unconsolidated investments									0.0	0.0	0.0
Income from consolidated subsidiaries									(1,033.2)	(740.1)	(631.6)
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	0.0	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
Income before (provision for) benefit from income taxes									(1,033.2)	(740.1)	(631.6)
(Provision for) benefit from income taxes									0.0	0.0	0.0
Net income									(1,033.2)	(740.1)	(631.6)
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Preferred dividends and accretion of preferred stock issuance costs									0.0	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders									(1,033.2)	(740.1)	(631.6)
Rental [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									514.6	504.7	485.9
Cost goods and services sold									160.8	151.2	135.4
Rental [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Rental [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Rental [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									168.4	143.9	114.0
Cost goods and services sold									62.3	54.7	48.7
Rental [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									346.2	360.8	371.9
Cost goods and services sold									98.5	96.5	86.7
Rental [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Hotel [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									155.7	127.5	116.2
Cost goods and services sold									121.5	100.3	96.3
Hotel [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Hotel [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Hotel [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Hotel [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									155.7	127.5	116.2
Cost goods and services sold									121.5	100.3	96.3
Hotel [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Sale of real estate [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									56.8	111.5	29.3
Cost goods and services sold									52.5	80.2	22.1
Sale of real estate [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Sale of real estate [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Cost goods and services sold									0.0	0.0	0.0
Sale of real estate [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	2.3	12.2
Cost goods and services sold									0.0	1.8	9.6
Sale of real estate [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									56.8	109.2	17.1
Cost goods and services sold									52.5	78.4	12.5
Sale of real estate [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
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]
Condensed Financial Statements, Captions [Line Items]
Total revenue									45.3	42.9	46.4
Investment management, property services and research fees [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Investment management, property services and research fees [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Investment management, property services and research fees [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									41.9	34.7	40.8
Investment management, property services and research fees [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									3.4	8.2	5.6
Investment management, property services and research fees [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Loan purchases, loan originations, and other [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									1.1	15.2	12.6
Loan purchases, loan originations, and other [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Loan purchases, loan originations, and other [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.1
Loan purchases, loan originations, and other [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.1	0.5	1.1
Loan purchases, loan originations, and other [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									1.0	14.7	11.4
Loan purchases, loan originations, and other [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Total revenue									0.0	0.0	0.0
Commission and marketing [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									5.9	7.2	8.0
Commission and marketing [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									0.0	0.0	0.0
Commission and marketing [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									0.0	0.0	0.0
Commission and marketing [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									5.9	7.0	7.3
Commission and marketing [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									0.0	0.2	0.7
Commission and marketing [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									0.0	0.0	0.0
Compensation and related [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									168.8	177.2	186.5
Compensation and related [Member] | Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									37.1	38.4	65.1
Compensation and related [Member] | Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									71.3	78.3	66.4
Compensation and related [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									55.1	52.8	47.5
Compensation and related [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									5.3	7.7	7.5
Compensation and related [Member] | Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Cost goods and services sold									$ 0.0	$ 0.0	$ 0.0