GUARANTOR AND NON-GUARANTOR FINANCIAL STATEMENTS - Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue
Rental									$ 504.7	$ 485.9	$ 404.8
Hotel									127.5	116.2	106.4
Sale of real estate									111.5	29.3	3.7
Investment management, property services, and research fees									51.7	59.4	69.3
Loan purchases, loan originations, and other									15.2	12.6	19.5
Total revenue	$ 181.5	$ 277.2	$ 177.8	$ 174.2	$ 180.4	$ 174.3	$ 176.5	$ 172.2	810.6	703.4	603.7
Operating expenses
Rental operating									151.2	135.4	108.0
Hotel operating									100.3	96.3	89.9
Cost of real estate sold									(80.2)	(22.1)	(2.6)
Commission and marketing									7.2	8.0	7.3
Compensation and related									177.2	186.5	154.8
General and administrative									42.2	45.4	43.8
Depreciation and amortization									212.5	198.2	166.3
Total operating expenses	206.0	231.2	178.3	155.4	194.3	166.1	168.6	162.9	770.8	691.9	572.7
Income from unconsolidated investments	20.2	12.9	13.4	22.6	67.3	31.7	8.4	19.2	69.0	126.6	97.4
Income from consolidated subsidiaries									0.0	0.0	0.0
Operating income	(4.3)	58.9	12.9	41.4	53.4	39.9	16.3	28.5	108.8	138.1	128.4
Non-operating income (expense)
Gain on sale of real estate									226.7	130.7	72.4
Acquisition-related gains									0.0	16.2	108.1
Acquisition-related expenses									(4.4)	(9.5)	(37.3)
Interest expense									(217.7)	(191.6)	(156.7)
Other income (loss)									8.3	6.6	(2.5)
Income before benefit from (provision for) income taxes	88.2	6.1	30.6	(3.0)	57.1	18.6	(6.1)	20.9	121.7	90.5	112.4
Benefit from (provision for) income taxes	17.2	3.7	(8.8)	4.2	(11.9)	(5.5)	3.9	(0.5)	16.3	(14.0)	(53.4)
Net income	105.4	9.8	21.8	1.2	45.2	13.1	(2.2)	20.4	138.0	76.5	59.0
Net (income) loss attributable to the noncontrolling interests	(6.2)	(18.7)	(12.4)	(0.2)	(29.6)	(15.1)	1.1	(27.3)	(37.5)	(70.9)	15.7
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									100.5	5.6	74.7
Preferred dividends and accretion of preferred stock issuance costs	0.0	0.0	0.0	0.0	(1.2)	(0.5)	(0.5)	(0.6)	0.0	(2.8)	(3.6)
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders	$ 99.2	$ (8.9)	$ 9.4	$ 1.0	$ 14.4	$ (2.5)	$ (1.6)	$ (7.5)	100.5	2.8	71.1
Reportable Legal Entities [Member] | Parent [Member]
Revenue
Rental									0.0	0.0	0.0
Hotel									0.0	0.0	0.0
Sale of real estate									0.0	0.0	0.0
Investment management, property services, and research fees									0.0	0.0	0.0
Loan purchases, loan originations, and other									0.0	0.0	0.0
Total revenue									0.0	0.0	0.0
Operating expenses
Rental operating									0.0	0.0	0.0
Hotel operating									0.0	0.0	0.0
Cost of real estate sold									0.0	0.0	0.0
Commission and marketing									0.0	0.0	0.0
Compensation and related									38.4	65.1	30.8
General and administrative									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Total operating expenses									38.4	65.1	30.8
Income from unconsolidated investments									0.0	0.0	0.0
Income from consolidated subsidiaries									176.4	141.6	89.8
Operating income									138.0	76.5	59.0
Non-operating income (expense)
Gain on sale of real estate									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 (loss)									0.0	0.0	0.0
Income before benefit from (provision for) income taxes									138.0	76.5	59.0
Benefit from (provision for) income taxes									0.0	0.0	0.0
Net income									138.0	76.5	59.0
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									138.0	76.5	59.0
Preferred dividends and accretion of preferred stock issuance costs									0.0	(2.8)	(3.6)
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders									138.0	73.7	55.4
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Revenue
Rental									0.0	0.0	0.0
Hotel									0.0	0.0	0.0
Sale of real estate									0.0	0.0	0.0
Investment management, property services, and research fees									0.0	0.0	0.0
Loan purchases, loan originations, and other									0.0	0.1	0.1
Total revenue									0.0	0.1	0.1
Operating expenses
Rental operating									0.0	0.0	0.0
Hotel operating									0.0	0.0	0.0
Cost of real estate sold									0.0	0.0	0.0
Commission and marketing									0.0	0.0	1.6
Compensation and related									78.3	66.4	50.1
General and administrative									14.0	15.9	15.0
Depreciation and amortization									1.4	1.3	0.8
Total operating expenses									93.7	83.6	67.5
Income from unconsolidated investments									3.7	5.6	0.4
Income from consolidated subsidiaries									307.5	285.1	220.1
Operating income									217.5	207.2	153.1
Non-operating income (expense)
Gain on sale of real estate									0.0	0.0	0.0
Acquisition-related gains									0.0	0.0	0.0
Acquisition-related expenses									0.0	0.0	(0.8)
Interest expense									(72.1)	(54.2)	(47.9)
Other income (loss)									9.9	7.7	1.0
Income before benefit from (provision for) income taxes									155.3	160.7	105.4
Benefit from (provision for) income taxes									21.1	(19.1)	(15.6)
Net income									176.4	141.6	89.8
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									176.4	141.6	89.8
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									176.4	141.6	89.8
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Revenue
Rental									143.9	114.0	65.4
Hotel									0.0	0.0	0.0
Sale of real estate									2.3	12.2	0.0
Investment management, property services, and research fees									43.4	53.7	66.1
Loan purchases, loan originations, and other									0.5	1.1	1.2
Total revenue									190.1	181.0	132.7
Operating expenses
Rental operating									54.7	48.7	25.3
Hotel operating									0.0	0.0	0.0
Cost of real estate sold									(1.8)	(9.6)
Commission and marketing									7.0	7.3	4.6
Compensation and related									52.8	47.5	65.4
General and administrative									17.6	16.3	16.7
Depreciation and amortization									50.1	39.5	20.8
Total operating expenses									184.0	168.9	132.8
Income from unconsolidated investments									33.0	64.0	79.3
Income from consolidated subsidiaries									256.2	204.9	95.9
Operating income									295.3	281.0	175.1
Non-operating income (expense)
Gain on sale of real estate									46.6	19.6	0.1
Acquisition-related gains									0.0	7.6	70.0
Acquisition-related expenses									(1.3)	(2.3)	(0.7)
Interest expense									(38.0)	(25.4)	(15.8)
Other income (loss)									1.6	(2.7)	(1.7)
Income before benefit from (provision for) income taxes									304.2	277.8	227.0
Benefit from (provision for) income taxes									3.3	7.3	(6.9)
Net income									307.5	285.1	220.1
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									307.5	285.1	220.1
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									307.5	285.1	220.1
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Revenue
Rental									360.8	371.9	339.4
Hotel									127.5	116.2	106.4
Sale of real estate									109.2	17.1	3.7
Investment management, property services, and research fees									8.3	5.7	3.2
Loan purchases, loan originations, and other									14.7	11.4	18.2
Total revenue									620.5	522.3	470.9
Operating expenses
Rental operating									96.5	86.7	82.7
Hotel operating									100.3	96.3	89.9
Cost of real estate sold									(78.4)	(12.5)	(2.6)
Commission and marketing									0.2	0.7	1.1
Compensation and related									7.7	7.5	8.5
General and administrative									10.6	13.2	12.1
Depreciation and amortization									161.0	157.4	144.7
Total operating expenses									454.7	374.3	341.6
Income from unconsolidated investments									32.3	57.0	17.7
Income from consolidated subsidiaries									0.0	0.0	0.0
Operating income									198.1	205.0	147.0
Non-operating income (expense)
Gain on sale of real estate									180.1	111.1	72.3
Acquisition-related gains									0.0	8.6	38.1
Acquisition-related expenses									(3.1)	(7.2)	(35.8)
Interest expense									(107.6)	(112.0)	(93.0)
Other income (loss)									(3.2)	1.6	(1.8)
Income before benefit from (provision for) income taxes									264.3	207.1	126.8
Benefit from (provision for) income taxes									(8.1)	(2.2)	(30.9)
Net income									256.2	204.9	95.9
Net (income) loss attributable to the noncontrolling interests									(37.5)	(70.9)	15.7
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									218.7	134.0	111.6
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									218.7	134.0	111.6
Elimination [Member]
Revenue
Rental									0.0	0.0	0.0
Hotel									0.0	0.0	0.0
Sale of real estate									0.0	0.0	0.0
Investment management, property services, and research fees									0.0	0.0	0.0
Loan purchases, loan originations, and other									0.0	0.0	0.0
Total revenue									0.0	0.0	0.0
Operating expenses
Rental operating									0.0	0.0	0.0
Hotel operating									0.0	0.0	0.0
Cost of real estate sold									0.0	0.0	0.0
Commission and marketing									0.0	0.0	0.0
Compensation and related									0.0	0.0	0.0
General and administrative									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Total operating expenses									0.0	0.0	0.0
Income from unconsolidated investments									0.0	0.0	0.0
Income from consolidated subsidiaries									(740.1)	(631.6)	(405.8)
Operating income									(740.1)	(631.6)	(405.8)
Non-operating income (expense)
Gain on sale of real estate									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 (loss)									0.0	0.0	0.0
Income before benefit from (provision for) income taxes									(740.1)	(631.6)	(405.8)
Benefit from (provision for) income taxes									0.0	0.0	0.0
Net income									(740.1)	(631.6)	(405.8)
Net (income) loss attributable to the noncontrolling interests									0.0	0.0	0.0
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc.									(740.1)	(631.6)	(405.8)
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									$ (740.1)	$ (631.6)	$ (405.8)