Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014 office sqft	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014 segment office sqft	Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Number of Operating Segments				2
Average Ownership Interest in Investments				34.00%
Area of real estate property	69,000,000			69,000,000
Number of Offices	25			25
Investment management, property services and research fees (includes $33.3, $13.8, $40.6, and $22.2 of related party fees)	$ 39.0	$ 19.5	$ 19.5	$ 52.1	$ 33.1
Investment management, property services, and research fees— related party	33.3	13.8		40.6	22.2
Rental and hotel	42.6	10.3	10.3	67.8	16.8
Sale of real estate	6.1	6.1	6.1	17.4	8.5
Loans and other	4.3	0.5	0.5	6.0	0.9
Total revenue	92.0	36.4	36.4	143.3	59.3
Operating expenses	(63.3)	(35.7)		(116.7)	(60.2)
Depreciation and amortization	(25.3)	(4.4)	(4.4)	(32.6)	(7.5)
Total operating expenses	(88.6)	(40.1)	(40.1)	(149.3)	(67.7)
Income from unconsolidated investments	31.0	14.8	14.8	33.8	16.9
Operating income	34.4	11.1	11.1	27.8	8.5
Acquisition-related gains	86.0	0	(0.5)	170.3	9.5
Acquisition-related expenses	(7.6)	(0.5)		(11.6)	(0.5)
Interest expense-investment	(11.1)	(2.8)	(2.8)	(16.4)	(4.6)
Interest expense-corporate	(14.7)	(9.7)	(9.7)	(25.2)	(19.4)
Other	2.1	0.1	0.1	2.9	0.4
Income (loss) before (provision for) benefit from income taxes	89.1	(1.8)	(1.8)	147.8	(6.1)
(Provision for) benefit from income taxes	(25.4)	0.5	0.5	(34.2)	2.2
Net income (loss)	63.7	(1.3)		113.6	(3.9)
Net (income) loss attributable to the noncontrolling interests	(25.3)	0.9	0.9	(62.7)	1.9
Preferred dividends and accretion of preferred stock issuance costs	(2.1)	(2.1)	(2.1)	(4.1)	(4.1)
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders	36.3	(2.5)	(2.5)	46.8	(6.1)
Total assets	5,354.7			5,354.7		1,798.8
Investments [Member]
Segment Reporting Information [Line Items]
Rental and hotel	42.6	10.3		67.8	16.8
Sale of real estate	6.1	6.1		17.4	8.5
Loans and other	4.3	0.5		6.0	0.9
Total revenue	53.0	16.9		91.2	26.2
Operating expenses	(39.0)	(18.7)		(75.1)	(31.3)
Depreciation and amortization	(25.3)	(4.4)		(32.6)	(7.5)
Income from unconsolidated investments	29.9	14.8		31.7	16.9
Operating income	18.6	8.6		15.2	4.3
Acquisition-related gains	86.0	0		170.3	9.5
Acquisition-related expenses	(7.6)	(0.5)		(11.6)	(0.5)
Interest expense-investment	(11.1)	(2.8)		(16.4)	(4.6)
Other	2.1	0.1		2.9	0.4
Net income (loss)	88.0	5.4		160.4	9.1
Net (income) loss attributable to the noncontrolling interests	(25.3)	0.9		(62.7)	1.9
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders	62.7	6.3		97.7	11.0
Total assets	4,893.0			4,893.0		1,607.5
Services [Member]
Segment Reporting Information [Line Items]
Investment management, property services and research fees (includes $33.3, $13.8, $40.6, and $22.2 of related party fees)	39.0	19.5		52.1	33.1
Investment management, property services, and research fees— related party	33.3	13.8		40.6	22.2
Total revenue	39.0	19.5		52.1	33.1
Operating expenses	(14.7)	(9.9)		(25.9)	(18.2)
Income from unconsolidated investments	1.1	0		2.1	0
Operating income	25.4	9.6		28.3	14.9
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders	25.4	9.6		28.3	14.9
Total assets	104.8			104.8		49.3
Corporate [Member]
Segment Reporting Information [Line Items]
Operating expenses	(9.6)	(7.2)		(15.9)	(10.9)
Operating income	(9.6)	(7.2)		(15.9)	(10.9)
Interest expense-corporate	(14.7)	(9.7)		(25.2)	(19.4)
Other	0	0.1		0	0.2
Income (loss) before (provision for) benefit from income taxes	(24.3)	(16.8)		(41.1)	(30.1)
(Provision for) benefit from income taxes	(25.4)	0.5		(34.2)	2.2
Net income (loss)	(49.7)	(16.3)		(75.3)	(27.9)
Preferred dividends and accretion of preferred stock issuance costs	(2.1)	(2.1)		(4.1)	(4.1)
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders	(51.8)	(18.4)		(79.4)	(32.0)
Total assets	$ 356.9			$ 356.9		$ 142.0