Guarantor and Non-Guarantor Financial Statements - Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		$ 29.9	$ 63.7	$ 25.6	$ 113.6
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		68.7	23.1	(36.2)	21.9
Unrealized gain on marketable securities		0.0	0.0	0.1	0.0
Amounts reclassified out of AOCI during the period		10.3	(8.3)	10.0	(7.1)
Unrealized currency derivative contracts gain (loss)		(3.4)	(2.1)	15.0	(3.6)
Total other comprehensive gain (loss) for the period		75.6	12.7	(11.1)	11.2
Comprehensive income		105.5	76.4	14.5	124.8
Comprehensive loss (income) attributable to noncontrolling interests	[1]	(58.9)	(44.1)	10.4	(81.5)
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		46.6	32.3	24.9	43.3
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		29.9	63.6	25.6	113.6
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		68.7	23.1	(36.2)	21.9
Unrealized gain on marketable securities				0.1
Amounts reclassified out of AOCI during the period		10.3	(8.3)	10.0	(7.1)
Unrealized currency derivative contracts gain (loss)		(3.3)	(2.1)	15.0	(3.6)
Total other comprehensive gain (loss) for the period		75.7	12.7	(11.1)	11.2
Comprehensive income		105.6	76.3	14.5	124.8
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		105.6	76.3	14.5	124.8
Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		36.8	65.3	39.7	116.9
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		68.7	23.1	(36.2)	21.9
Unrealized gain on marketable securities				0.0
Amounts reclassified out of AOCI during the period		10.3	(8.3)	10.0	(7.1)
Unrealized currency derivative contracts gain (loss)		(3.3)	(2.1)	15.1	(3.6)
Total other comprehensive gain (loss) for the period		75.7	12.7	(11.1)	11.2
Comprehensive income		112.5	78.0	28.6	128.1
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		112.5	78.0	28.6	128.1
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		92.0	127.7	104.6	209.6
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		33.7	29.1	(8.4)	23.9
Unrealized gain on marketable securities				0.0
Amounts reclassified out of AOCI during the period		0.0	(8.3)	(0.3)	(8.3)
Unrealized currency derivative contracts gain (loss)		(23.8)	(3.6)	2.5	(1.2)
Total other comprehensive gain (loss) for the period		9.9	17.2	(6.2)	14.4
Comprehensive income		101.9	144.9	98.4	224.0
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		101.9	144.9	98.4	224.0
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		81.2	75.8	84.1	153.0
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		135.3	(3.1)	114.5	(3.9)
Unrealized gain on marketable securities				0.1
Amounts reclassified out of AOCI during the period		10.3	0.0	10.3	1.2
Unrealized currency derivative contracts gain (loss)		20.4	(1.2)	12.6	(1.2)
Total other comprehensive gain (loss) for the period		166.0	(4.3)	137.5	(3.9)
Comprehensive income		247.2	71.5	221.6	149.1
Comprehensive loss (income) attributable to noncontrolling interests		(58.9)	(44.1)	10.4	(81.5)
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		188.3	27.4	232.0	67.6
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Net (loss) income		(210.0)	(268.7)	(228.4)	(479.5)
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(237.7)	(49.1)	(69.9)	(41.9)
Unrealized gain on marketable securities				(0.1)
Amounts reclassified out of AOCI during the period		(20.6)	16.6	(20.0)	14.2
Unrealized currency derivative contracts gain (loss)		6.6	6.9	(30.2)	6.0
Total other comprehensive gain (loss) for the period		(251.7)	(25.6)	(120.2)	(21.7)
Comprehensive income		(461.7)	(294.3)	(348.6)	(501.2)
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income attributable to Kennedy-Wilson Holdings, Inc. common shareholders		$ (461.7)	$ (294.3)	$ (348.6)	$ (501.2)

[1] Comprehensive income attributable to noncontrolling interest includes allocation of unrealized currency translation losses and currency derivative contracts.