Guarantor and Non-Guarantor Financial Statements - Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		$ 5.1	$ (3.0)	$ 30.7	$ 110.6
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(51.8)	(89.0)	(88.0)	(67.1)
Unrealized (loss) gain on marketable securities		0.0	(1.1)	0.1	(1.1)
Amounts reclassified out of AOCI during the period		(0.3)	0.0	9.7	(7.1)
Unrealized currency derivative contracts gain (loss)		(8.3)	20.1	6.7	16.5
Total other comprehensive (loss) gain for the period		(60.4)	(70.0)	(71.5)	(58.8)
Comprehensive (loss) income		(55.3)	(73.0)	(40.8)	51.8
Comprehensive loss (income) attributable to noncontrolling interests	[1]	67.9	58.0	78.3	(23.5)
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		12.6	(15.0)	37.5	28.3
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		5.1	(3.0)	30.7	110.6
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(51.8)	(89.0)	(88.0)	(67.1)
Unrealized (loss) gain on marketable securities			(1.1)	0.1	(1.1)
Amounts reclassified out of AOCI during the period		(0.3)	0.0	9.7	(7.1)
Unrealized currency derivative contracts gain (loss)		(8.3)	20.1	6.7	16.5
Total other comprehensive (loss) gain for the period		(60.4)	(70.0)	(71.5)	(58.8)
Comprehensive (loss) income		(55.3)	(73.0)	(40.8)	51.8
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		(55.3)	(73.0)	(40.8)	51.8
Kennedy-Wilson, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		10.6	2.4	50.3	119.3
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(51.8)	(89.0)	(88.0)	(67.1)
Unrealized (loss) gain on marketable securities			(1.1)	0.1	(1.1)
Amounts reclassified out of AOCI during the period		(0.3)	0.0	9.7	(7.1)
Unrealized currency derivative contracts gain (loss)		(8.3)	20.1	6.7	16.5
Total other comprehensive (loss) gain for the period		(60.4)	(70.0)	(71.5)	(58.8)
Comprehensive (loss) income		(49.8)	(67.6)	(21.2)	60.5
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		(49.8)	(67.6)	(21.2)	60.5
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		44.0	35.5	148.7	245.0
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(1.0)	(21.4)	(9.4)	2.5
Unrealized (loss) gain on marketable securities			0.0	0.0	0.0
Amounts reclassified out of AOCI during the period		(0.3)	9.5	(0.6)	1.2
Unrealized currency derivative contracts gain (loss)		5.8	6.5	8.3	5.3
Total other comprehensive (loss) gain for the period		4.5	(5.4)	(1.7)	9.0
Comprehensive (loss) income		48.5	30.1	147.0	254.0
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0	0.0	0.0
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		48.5	30.1	147.0	254.0
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		(35.0)	30.3	49.0	183.3
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		(138.3)	(12.6)	(23.8)	(16.5)
Unrealized (loss) gain on marketable securities			0.0	0.0	0.0
Amounts reclassified out of AOCI during the period		0.0	(9.5)	10.3	(8.3)
Unrealized currency derivative contracts gain (loss)		(14.1)	11.3	(1.6)	10.1
Total other comprehensive (loss) gain for the period		(152.4)	(10.8)	(15.1)	(14.7)
Comprehensive (loss) income		(187.4)	19.5	33.9	168.6
Comprehensive loss (income) attributable to noncontrolling interests		67.9	58.0	78.3	(23.5)
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		(119.5)	77.5	112.2	145.1
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		(19.6)	(68.2)	(248.0)	(547.6)
Other comprehensive income (loss), net of tax:
Unrealized foreign currency translation (loss) gain		191.1	123.0	121.2	81.1
Unrealized (loss) gain on marketable securities			1.1	(0.1)	1.1
Amounts reclassified out of AOCI during the period		0.6	0.0	(19.4)	14.2
Unrealized currency derivative contracts gain (loss)		16.6	(37.9)	(13.4)	(31.9)
Total other comprehensive (loss) gain for the period		208.3	86.2	88.3	64.5
Comprehensive (loss) income		188.7	18.0	$ (159.7)	(483.1)
Comprehensive loss (income) attributable to noncontrolling interests		0.0	0.0		0.0
Comprehensive income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders		$ 188.7	$ 18.0	$ (159.7)	$ (483.1)

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