Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc. common shareholders	$ (8.9)	$ (2.5)	$ 1.3	$ (11.6)
Dividends allocated to participating securities	(0.2)	(0.4)	(0.7)	(1.3)
Net (loss) income attributable to Kennedy-Wilson Holdings, Inc. common shareholders, net of allocation to participating securities	(9.1)	(2.9)	0.6	(12.9)
Dividends declared on common shares	(19.3)	(15.6)	(57.9)	(46.7)
Undistributed losses attributable to Kennedy-Wilson Holdings, Inc. common shareholders, net of allocation to participating securities	$ (28.4)	$ (18.5)	$ (57.3)	$ (59.6)
Distributed earnings per share (in dollars per share)	$ 0.17	$ 0.14	$ 0.52	$ 0.42
Undistributed losses per share (in dollars per share)	(0.25)	(0.17)	(0.51)	(0.54)
(Loss) income per basic (in dollars per share)	(0.08)	(0.03)	0.01	(0.12)
(Loss) income per diluted (in dollars per share)	$ (0.08)	$ (0.03)	$ 0.01	$ (0.12)
Weighted average shares outstanding for basic (in shares)	111,966,716	108,634,228	111,955,924	108,966,540
Weighted average shares outstanding for diluted (in shares)	111,966,716	108,634,228	111,955,924	108,966,540
Dividends declared per common share (in dollars per share)	$ 0.17	$ 0.14	$ 0.51	$ 0.42
Potentially dilutive securities (in shares)	1,145,032	3,782,564	1,028,565	3,493,709