Consolidated Statements of Equity (USD $) In Millions, except Share data, unless otherwise specified	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Kennedy Wilson Europe Real Estate, Pllc [Member]	Kennedy Wilson Europe Real Estate, Pllc [Member] Additional Paid-in Capital [Member]	Kennedy Wilson Europe Real Estate, Pllc [Member] Noncontrolling Interest [Member]
Balance at Dec. 31, 2011	$ 413.6	$ 0	$ 0	$ 407.3	$ 9.7	$ 5.0	$ (11.8)	$ 3.4
Balance, common shares (in shares) at Dec. 31, 2011			51,825,998
Balance, preferred shares (in shares) at Dec. 31, 2011		132,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock (in shares)			(3,400)
Repurchase of common shares	0
Repurchase of warrants	(1.6)			(1.6)
Issuance of common stock (in shares)	8,625,000		8,625,000
Issuance of common stock	106.3			106.3
Common stock issued under amended and restated equity participation plan (in shares)			3,175,000
Common stock issued under amended and restated equity participation plan	0			0
Stock compensation expense	3.5			3.5
Other comprehensive income (loss):
Unrealized losses on marketable securities, net of tax	3.3					3.3
Unrealized foreign currency translation gain, net of tax	(1.4)					(1.4)
Unrealized foreign currency derivative gain, net of tax	5.7					5.7
Preferred stock dividends paid	(8.1)				(8.1)
Common stock dividends	(11.7)				(11.7)
Net income	6.7				4.2			2.5
Acquistion of noncontrolling interests (in shares)			150,000
Acquistion of noncontrolling interests	(0.6)			(2.7)			2.0	0.1
Consolidation of Fund II	7.6							7.6
Contributions from noncontrolling interests	0.4							0.4
Distributions to noncontrolling interests	(4.9)							(4.9)
Balance at Dec. 31, 2012	518.8	0	0	512.8	(5.9)	12.6	(9.8)	9.1
Balance, common shares (in shares) at Dec. 31, 2012			63,772,598
Balance, preferred shares (in shares) at Dec. 31, 2012		132,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of warrants	(1.4)			(1.4)
Issuance of common stock (in shares)	17,250,000		17,250,000
Issuance of common stock	275.9			275.9
Exercise of warrants into common shares (in shares)	2,684,670		1,771,862
Exercise of warrants into common shares	15.4			15.4
Shares forfeited, net of 3,000 shares of common stock issued under the 2009 Equity Participation Plan (in shares)	(146,638)
Retirement of common shares held in treasury				(9.8)			9.8
Common stock issued under amended and restated equity participation plan (in shares)			(10,038)
Common stock issued under amended and restated equity participation plan	0			0
Shares retired due to RSG Vesting (in shares)			(191,815)
Shares retired due to RSG Vesting	(3.8)			(3.8)
Stock compensation expense	7.5			7.5
RSG plan modification	4.7			4.7
Other comprehensive income (loss):
Unrealized losses on marketable securities, net of tax	0
Unrealized foreign currency translation gain, net of tax	(6.5)					(6.5)
Unrealized foreign currency derivative gain, net of tax	3.1					3.1
Preferred stock dividends paid	(8.1)				(8.1)
Common stock dividends	(21.8)				(21.8)
Net income	13.9				(6.4)			20.3
Consolidation of Fund II	20.3							20.3
Contributions from noncontrolling interests	1.4							1.4
Distributions to noncontrolling interests	(0.5)							(0.5)
Balance at Dec. 31, 2013	818.9	0	0	801.3	(42.2)	9.2	0	50.6
Balance, common shares (in shares) at Dec. 31, 2013	82,592,607		82,592,607
Balance, preferred shares (in shares) at Dec. 31, 2013		132,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			9,201,250
Issuance of common stock	190.6			190.6
Shares granted (in shares)			3,147,500
Exercise of warrants into common shares (in shares)			1,472,146
Shares forfeited, net of 3,000 shares of common stock issued under the 2009 Equity Participation Plan (in shares)			(2,475)
Shares forfeited, net of 3,000 shares of common stock issued under the 2009 Equity Participation Plan	0
Shares retired due to RSG Vesting (in shares)			(319,582)
Shares retired due to RSG Vesting	(8.1)			(8.1)
Stock based compensation	15.8			15.8
Other comprehensive income (loss):
Unrealized losses on marketable securities, net of tax	(0.2)					(0.2)
Unrealized foreign currency translation gain, net of tax	(141.1)					(46.7)		(94.4)
Unrealized foreign currency derivative gain, net of tax	20.1					9.5		10.6
Preferred stock dividends paid	(8.1)				(8.1)
Common stock dividends	(33.6)				(33.6)
Net income	90.1				21.9			68.2
Consolidation of Fund II	291.8							291.8
Contributions from noncontrolling interests	30.9							30.9	1,885.6	(8.3)	1,893.9
Distributions to noncontrolling interests	(57.7)							(57.7)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests									(51.1)
Balance at Dec. 31, 2014	3,043.9	0	0	991.3	(62.0)	(28.2)	0	2,142.8
Balance, common shares (in shares) at Dec. 31, 2014	96,091,446		96,091,446
Balance, preferred shares (in shares) at Dec. 31, 2014		132,550
Balance at Mar. 31, 2014
Other comprehensive income (loss):
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests									(51.1)
Balance at Dec. 31, 2014		0					0
Balance, preferred shares (in shares) at Dec. 31, 2014		132,550
Balance at Sep. 30, 2014
Other comprehensive income (loss):
Net income	(20.5)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests									(75.0)
Balance at Dec. 31, 2014	$ 3,043.9	$ 0					$ 0
Balance, common shares (in shares) at Dec. 31, 2014	96,091,446
Balance, preferred shares (in shares) at Dec. 31, 2014		132,550