Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders	$ 14.9	$ (2.2)	$ 42.6	$ 44.6
Net income (loss) and dividends allocated to participating securities	(0.6)	(0.5)	(1.9)	(2.6)
Net income (loss) attributable to Kennedy-Wilson Holdings, Inc. common shareholders, net of allocation to participating securities	14.3	(2.7)	40.7	42.0
Dividends declared on common shares	(13.0)	(8.1)	(37.8)	(24.1)
Undistributed earnings attributable to Kennedy-Wilson Holdings, Inc. common shareholders, net of allocation to participating securities	$ 1.3	$ (10.8)	$ 2.9	$ 17.9
Distributed earnings per share (in dollars per share)	$ 0.12	$ 0.09	$ 0.36	$ 0.27
Undistributed earnings per share (in dollars per share)	0.01	(0.12)	0.04	0.20
Income (loss) per basic (in dollars per share)	0.13	(0.03)	0.40	0.47
Income (loss) per diluted (in dollars per share)	$ 0.13	$ (0.03)	$ 0.40	$ 0.47
Weighted average shares outstanding for basic (in shares)	107,433,124	89,267,838	101,361,606	88,854,215
Weighted average shares outstanding for diluted (in shares)	107,433,124	89,267,838	105,517,172	90,169,008
Dividends declared per common share (in dollars per share)	$ 0.12	$ 0.09	$ 0.36	$ 0.27
Potentially dilutive securities (in shares)	3,538,420	12,993,531	3,163,589