GUARANTOR AND NON-GUARANTOR FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents		$ 351.3	$ 885.7	$ 731.6	$ 937.7
Accounts receivable		62.7	44.0
Loan purchases and originations		84.7	87.7
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		6,443.7	5,814.2
Unconsolidated investments		486.4	555.6
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		296.0	269.4
Total assets	[1]	7,724.8	7,656.6
Liabilities
Accounts payable		19.5	11.2
Accrued expenses and other liabilities		465.9	412.1
Total liabilities	[1]	6,147.3	5,313.5
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,365.6	1,048.0
Noncontrolling interests		211.9	1,295.1
Total equity		1,577.5	2,343.1	2,865.1	3,043.9
Total liabilities and equity		7,724.8	7,656.6
Mortgages [Member]
Liabilities
Long-term debt		3,156.6	2,770.4
Unsecured Debt [Member]
Liabilities
Long-term debt		1,179.4	934.1
Unsecured Bonds [Member]
Liabilities
Long-term debt		1,325.9	1,185.7
Reportable Legal Entities [Member] | Parent [Member]
Assets
Cash and cash equivalents		0.0	0.0	0.0	0.0
Accounts receivable		0.0	0.0
Loan purchases and originations		0.0	0.0
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0	0.0
Unconsolidated investments		0.0	0.0
Investments in and advances to consolidated subsidiaries		1,394.5	1,063.8
Other assets		0.0	0.0
Total assets		1,394.5	1,063.8
Liabilities
Accounts payable		0.0	0.0
Accrued expenses and other liabilities		28.9	15.8
Total liabilities		28.9	15.8
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,365.6	1,048.0
Noncontrolling interests		0.0	0.0
Total equity		1,365.6	1,048.0
Total liabilities and equity		1,394.5	1,063.8
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Assets
Cash and cash equivalents		33.4	106.0	80.2	38.2
Accounts receivable		0.9	0.0
Loan purchases and originations		0.0	0.3
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0	0.0
Unconsolidated investments		20.2	18.8
Investments in and advances to consolidated subsidiaries		2,642.1	2,073.1
Other assets		0.0	0.2
Total assets		2,696.6	2,198.4
Liabilities
Accounts payable		0.8	0.5
Accrued expenses and other liabilities		121.9	200.0
Total liabilities		1,302.1	1,134.6
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,394.5	1,063.8
Noncontrolling interests		0.0	0.0
Total equity		1,394.5	1,063.8
Total liabilities and equity		2,696.6	2,198.4
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		54.9	45.4	37.0	21.0
Accounts receivable		10.1	10.2
Loan purchases and originations		5.8	12.1
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		1,750.0	1,482.5
Unconsolidated investments		298.3	380.0
Investments in and advances to consolidated subsidiaries		1,629.4	1,171.7
Other assets		73.1	66.9
Total assets		3,821.6	3,168.8
Liabilities
Accounts payable		2.5	1.6
Accrued expenses and other liabilities		39.7	157.2
Total liabilities		1,179.5	1,095.6
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		2,642.1	2,073.2
Noncontrolling interests		0.0	0.0
Total equity		2,642.1	2,073.2
Total liabilities and equity		3,821.6	3,168.8
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		263.0	734.3	$ 614.4	$ 878.5
Accounts receivable		51.7	33.8
Loan purchases and originations		78.9	75.3
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		4,693.7	4,331.7
Unconsolidated investments		167.9	156.8
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		222.9	202.3
Total assets		5,478.1	5,534.2
Liabilities
Accounts payable		16.2	9.1
Accrued expenses and other liabilities		275.4	39.1
Total liabilities		3,636.8	3,067.5
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,629.4	1,171.6
Noncontrolling interests		211.9	1,295.1
Total equity		1,841.3	2,466.7
Total liabilities and equity		5,478.1	5,534.2
Reportable Legal Entities [Member] | Mortgages [Member] | Parent [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Mortgages [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Mortgages [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		1,137.3	936.8
Reportable Legal Entities [Member] | Mortgages [Member] | Non-Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		2,019.3	1,833.6
Reportable Legal Entities [Member] | Unsecured Debt [Member] | Parent [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Debt [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		1,179.4	934.1
Reportable Legal Entities [Member] | Unsecured Debt [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Debt [Member] | Non-Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Bonds [Member] | Parent [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Bonds [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Bonds [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Unsecured Bonds [Member] | Non-Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		1,325.9	1,185.7
Elimination [Member]
Assets
Cash and cash equivalents		0.0	0.0
Accounts receivable		0.0	0.0
Loan purchases and originations		0.0	0.0
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0	0.0
Unconsolidated investments		0.0	0.0
Investments in and advances to consolidated subsidiaries		(5,666.0)	(4,308.6)
Other assets		0.0	0.0
Total assets		(5,666.0)	(4,308.6)
Liabilities
Accounts payable		0.0	0.0
Accrued expenses and other liabilities			0.0
Total liabilities		0.0	0.0
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		(5,666.0)	(4,308.6)
Noncontrolling interests		0.0	0.0
Total equity		(5,666.0)	(4,308.6)
Total liabilities and equity		(5,666.0)	(4,308.6)
Elimination [Member] | Mortgages [Member]
Liabilities
Long-term debt			0.0
Elimination [Member] | Unsecured Debt [Member]
Liabilities
Long-term debt		0.0	0.0
Elimination [Member] | Unsecured Bonds [Member]
Liabilities
Long-term debt		$ 0.0	$ 0.0

[1] The assets and liabilities as of December 31, 2017 include $904.4 million (including cash held by consolidated investments of $39.1 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $789.1 million) and $510.0 million (including investment debt of $475.3 million), respectively, from consolidated variable interest entities ("VIEs"). The assets and liabilities as of December 31, 2016 include $4.5 billion (including cash held by consolidated investments of $584.2 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $3.6 billion) and $2.7 billion (including investment debt of $2.4 billion), respectively, from VIEs. These assets can only be used to settle obligations of the consolidated VIEs, and the liabilities do not have recourse to the Company.