GUARANTOR AND NON-GUARANTOR FINANCIAL STATEMENTS - Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income	$ 158.9	$ 19.4	$ 141.2	$ 1.6	$ 32.9	$ 12.9	$ 167.3	$ (1.0)	$ 321.1	$ 212.1	$ 138.0
Other comprehensive income, net of tax:
Unrealized gain on marketable securities									0.0	0.0	0.2
Unrealized currency derivative contract gain (loss)									(0.7)
Unrealized foreign currency translation (loss) gain									(13.3)	(62.6)	155.3
Amounts reclassified from accumulated other comprehensive income									10.4	13.2	2.0
Unrealized currency derivative contracts gain (loss)										38.3	(68.3)
Unrealized forward contract forward currency gain									38.7
Total other comprehensive income (loss) for the year									35.1	(11.1)	89.2
Comprehensive income									356.2	201.0	227.2
Comprehensive income attributable to noncontrolling interests									(105.0)	(65.4)	(124.2)
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									251.2	135.6	103.0
Reportable Legal Entities [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									321.1	212.1	138.0
Other comprehensive income, net of tax:
Unrealized gain on marketable securities										0.0	0.2
Unrealized currency derivative contract gain (loss)									(0.7)
Unrealized foreign currency translation (loss) gain									(13.3)	(62.6)	155.3
Amounts reclassified from accumulated other comprehensive income									10.4	13.2	2.0
Unrealized currency derivative contracts gain (loss)										38.3	(68.3)
Unrealized forward contract forward currency gain									38.7
Total other comprehensive income (loss) for the year									35.1	(11.1)	89.2
Comprehensive income									356.2	201.0	227.2
Comprehensive income attributable to noncontrolling interests									0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									356.2	201.0	227.2
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									352.9	249.2	176.4
Other comprehensive income, net of tax:
Unrealized gain on marketable securities										0.0	0.2
Unrealized currency derivative contract gain (loss)									(0.7)
Unrealized foreign currency translation (loss) gain									(13.3)	(62.6)	155.3
Amounts reclassified from accumulated other comprehensive income									10.4	13.2	2.0
Unrealized currency derivative contracts gain (loss)										38.3	(68.3)
Unrealized forward contract forward currency gain									38.7
Total other comprehensive income (loss) for the year									35.1	(11.1)	89.2
Comprehensive income									388.0	238.1	265.6
Comprehensive income attributable to noncontrolling interests									0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									388.0	238.1	265.6
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									547.7	451.3	307.5
Other comprehensive income, net of tax:
Unrealized gain on marketable securities										0.0	0.0
Unrealized currency derivative contract gain (loss)									0.0
Unrealized foreign currency translation (loss) gain									16.1	(45.7)	30.6
Amounts reclassified from accumulated other comprehensive income									0.0	0.0	0.0
Unrealized currency derivative contracts gain (loss)										46.1	(21.9)
Unrealized forward contract forward currency gain									(15.4)
Total other comprehensive income (loss) for the year									0.7	0.4	8.7
Comprehensive income									548.4	451.7	316.2
Comprehensive income attributable to noncontrolling interests									0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									548.4	451.7	316.2
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									479.7	332.7	256.2
Other comprehensive income, net of tax:
Unrealized gain on marketable securities										0.0	0.0
Unrealized currency derivative contract gain (loss)									0.0
Unrealized foreign currency translation (loss) gain									(4.7)	(61.6)	458.7
Amounts reclassified from accumulated other comprehensive income									10.4	18.3	2.0
Unrealized currency derivative contracts gain (loss)										(7.8)	(46.4)
Unrealized forward contract forward currency gain									54.1
Total other comprehensive income (loss) for the year									59.8	(51.1)	414.3
Comprehensive income									539.5	281.6	670.5
Comprehensive income attributable to noncontrolling interests									(105.0)	(65.4)	(124.2)
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									434.5	216.2	546.3
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									(1,380.3)	(1,033.2)	(740.1)
Other comprehensive income, net of tax:
Unrealized gain on marketable securities										0.0	(0.2)
Unrealized currency derivative contract gain (loss)									0.7
Unrealized foreign currency translation (loss) gain									1.9	169.9	(644.6)
Amounts reclassified from accumulated other comprehensive income									(20.8)	(31.5)	(4.0)
Unrealized currency derivative contracts gain (loss)										(76.6)	136.6
Unrealized forward contract forward currency gain									(77.4)
Total other comprehensive income (loss) for the year									(95.6)	61.8	(512.2)
Comprehensive income									(1,475.9)	(971.4)	(1,252.3)
Comprehensive income attributable to noncontrolling interests									0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc.									$ (1,475.9)	$ (971.4)	$ (1,252.3)