UNAUDITED QUARTERLY INFORMATION (Details) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) asset $ / shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) asset $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 142.3	$ 143.0	$ 143.7	$ 140.7	$ 178.7	$ 185.8	$ 218.3	$ 190.7	$ 569.7	$ 772.4	$ 801.8
Expenses	155.0	147.9	143.8	153.1	187.8	177.2	212.5	188.9	599.8	766.4	770.8
Other income (expenses)(1)	177.9	34.5	162.2	18.0	66.3	11.2	190.9	(5.4)	179.7	78.7	77.8
Income (loss) before provision for income taxes	165.2	29.6	162.1	5.6	57.2	19.8	196.7	(3.6)	362.5	270.1	121.7
Benefit from (provision for) income taxes	(6.3)	(10.2)	(20.9)	(4.0)	(24.3)	(6.9)	(29.4)	2.6	(41.4)	(58.0)	16.3
Net income	158.9	19.4	141.2	1.6	32.9	12.9	167.3	(1.0)	321.1	212.1	138.0
Net income attributable to the noncontrolling interests	1.6	1.3	(90.4)	(6.9)	(2.2)	(0.8)	(57.7)	(1.4)	(94.4)	(62.1)	(37.5)
Preferred dividends and accretion of preferred stock issuance costs	(2.6)	0.0	0.0	0.0					(2.6)	0.0	0.0
Net income attributable to Kennedy-Wilson Holdings, Inc. common shareholders	$ 157.9	$ 20.7	$ 50.8	$ (5.3)	$ 30.7	$ 12.1	$ 109.6	$ (2.4)	$ 224.1	$ 150.0	$ 100.5
Basic (loss) earnings per share (in dollars per share) | $ / shares	$ 1.13	$ 0.15	$ 0.36	$ (0.04)	$ 0.21	$ 0.09	$ 0.77	$ (0.02)	$ 1.60	$ 1.04	$ 0.83
Income per diluted (in dollars per share) | $ / shares	$ 1.12	$ 0.15	$ 0.36	$ (0.04)	$ 0.21	$ 0.09	$ 0.77	$ (0.02)	$ 1.58	$ 1.04	$ 0.83
Deconsolidation, gain (loss)	$ 112.4
Real estate units sold, number of assets | asset	2								2
Ownership percentage sold of equity method investment	20.00%