Guarantor and Non-Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents		$ 447.1	$ 351.3
Accounts receivable		64.6	62.7
Loan purchases and originations		28.9	84.7
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		6,097.7	6,443.7
Unconsolidated investments		613.7	519.3
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		253.4	263.1
Total assets	[1]	7,505.4	7,724.8
Liabilities
Accounts payable		25.8	19.5
Accrued expenses and other liabilities		491.1	465.9
Total liabilities	[1]	6,055.7	6,147.3
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,270.3	1,365.6
Noncontrolling interests		179.4	211.9
Total equity		1,449.7	1,577.5
Total liabilities and equity		7,505.4	7,724.8
Mortgages [Member]
Liabilities
Long-term debt		2,993.9	3,156.6
Unsecured Debt [Member]
Liabilities
Long-term debt		1,249.9	1,179.4
Unsecured Bonds [Member]
Liabilities
Long-term debt		1,295.0	1,325.9
Reportable Legal Entities [Member] | Parent [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		1,297.8	1,394.5
Other assets		0.0	0.0
Total assets		1,297.8	1,394.5
Liabilities
Accounts payable		0.0	0.0
Accrued expenses and other liabilities		27.5	28.9
Total liabilities		27.5	28.9
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,270.3	1,365.6
Noncontrolling interests		0.0	0.0
Total equity		1,270.3	1,365.6
Total liabilities and equity		1,297.8	1,394.5
Reportable Legal Entities [Member] | Parent [Member] | Mortgages [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Parent [Member] | Unsecured Debt [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Parent [Member] | Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Assets
Cash and cash equivalents		18.6	33.4
Accounts receivable		0.0	0.9
Loan purchases and originations		0.5	0.0
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0	0.0
Unconsolidated investments		19.9	20.2
Investments in and advances to consolidated subsidiaries		2,652.9	2,642.1
Other assets		0.0	0.0
Total assets		2,691.9	2,696.6
Liabilities
Accounts payable		1.7	0.8
Accrued expenses and other liabilities		142.5	121.9
Total liabilities		1,394.1	1,302.1
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,297.8	1,394.5
Noncontrolling interests		0.0	0.0
Total equity		1,297.8	1,394.5
Total liabilities and equity		2,691.9	2,696.6
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | Mortgages [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | Unsecured Debt [Member]
Liabilities
Long-term debt		1,249.9	1,179.4
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		78.1	54.9
Accounts receivable		4.1	10.1
Loan purchases and originations		1.3	5.8
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		1,763.1	1,750.0
Unconsolidated investments		353.4	331.2
Investments in and advances to consolidated subsidiaries		1,605.0	1,629.4
Other assets		44.1	40.2
Total assets		3,849.1	3,821.6
Liabilities
Accounts payable		2.0	2.5
Accrued expenses and other liabilities		41.8	39.7
Total liabilities		1,196.2	1,179.5
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		2,652.9	2,642.1
Noncontrolling interests		0.0	0.0
Total equity		2,652.9	2,642.1
Total liabilities and equity		3,849.1	3,821.6
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Mortgages [Member]
Liabilities
Long-term debt		1,152.4	1,137.3
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Unsecured Debt [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		350.4	263.0
Accounts receivable		60.5	51.7
Loan purchases and originations		27.1	78.9
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		4,334.6	4,693.7
Unconsolidated investments		240.4	167.9
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		209.3	222.9
Total assets		5,222.3	5,478.1
Liabilities
Accounts payable		22.1	16.2
Accrued expenses and other liabilities		279.3	275.4
Total liabilities		3,437.9	3,636.8
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,605.0	1,629.4
Noncontrolling interests		179.4	211.9
Total equity		1,784.4	1,841.3
Total liabilities and equity		5,222.3	5,478.1
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | Mortgages [Member]
Liabilities
Long-term debt		1,841.5	2,019.3
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | Unsecured Debt [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | Unsecured Bonds [Member]
Liabilities
Long-term debt		1,295.0	1,325.9
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		(5,555.7)	(5,666.0)
Other assets		0.0	0.0
Total assets		(5,555.7)	(5,666.0)
Liabilities
Accounts payable		0.0	0.0
Accrued expenses and other liabilities		0.0	0.0
Total liabilities		0.0	0.0
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		(5,555.7)	(5,666.0)
Noncontrolling interests		0.0	0.0
Total equity		(5,555.7)	(5,666.0)
Total liabilities and equity		(5,555.7)	(5,666.0)
Elimination [Member] | Mortgages [Member]
Liabilities
Long-term debt		0.0	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 June 30, 2018 include $642.7 million (including cash held by consolidated investments of $27.5 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $565.8 million) and $335.5 million (including investment debt of $301.5 million), respectively, from consolidated variable interest entities ("VIEs"). 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 VIEs. These assets can only be used to settle obligations of the consolidated VIEs, and the liabilities do not have recourse to the Company.