Guarantor and Non-Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents		$ 404.0		$ 488.0
Accounts receivable		51.1		56.6
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		5,163.0		5,702.5
Unconsolidated investments		1,073.8		859.9
Investments in and advances to consolidated subsidiaries		0.0		0.0
Other assets		304.3		274.8
Total assets	[1]	6,996.2		7,381.8
Liabilities
Accounts payable		17.5		24.1
Accrued expenses and other liabilities		505.6		513.7
Total liabilities	[1]	5,705.9		5,950.6
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,246.2		1,246.7
Noncontrolling interests		44.1		184.5
Total equity		1,290.3	$ 1,302.2	1,431.2	$ 1,449.7	$ 1,566.7	$ 1,577.5
Total liabilities and equity		6,996.2		7,381.8
Mortgage Debt [Member]
Liabilities
Long-term debt		2,675.3		2,950.3
KW Unsecured Debt [Member]
Liabilities
Long-term debt		1,254.4		1,202.0
KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		1,253.1		1,260.5
Reportable Legal Entities [Member] | Parent [Member]
Assets
Cash and cash equivalents		0.0		0.0
Accounts receivable		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		1,276.6		1,276.9
Other assets		0.0		0.0
Total assets		1,276.6		1,276.9
Liabilities
Accounts payable		0.0		0.0
Accrued expenses and other liabilities		30.4		30.2
Total liabilities		30.4		30.2
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,246.2		1,246.7
Noncontrolling interests		0.0		0.0
Total equity		1,246.2		1,246.7
Total liabilities and equity		1,276.6		1,276.9
Reportable Legal Entities [Member] | Parent [Member] | Mortgage Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Parent [Member] | KW Unsecured Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Parent [Member] | KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Assets
Cash and cash equivalents		7.6		1.9
Accounts receivable		0.0		0.8
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0		0.0
Unconsolidated investments		18.7		19.2
Investments in and advances to consolidated subsidiaries		2,694.6		2,652.7
Other assets		0.0		0.9
Total assets		2,720.9		2,675.5
Liabilities
Accounts payable		1.1		0.7
Accrued expenses and other liabilities		188.8		195.9
Total liabilities		1,444.3		1,398.6
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,276.6		1,276.9
Noncontrolling interests		0.0		0.0
Total equity		1,276.6		1,276.9
Total liabilities and equity		2,720.9		2,675.5
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | Mortgage Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | KW Unsecured Debt [Member]
Liabilities
Long-term debt		1,254.4		1,202.0
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member] | KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		149.4		101.9
Accounts receivable		16.3		4.4
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		1,864.4		1,870.6
Unconsolidated investments		468.5		433.4
Investments in and advances to consolidated subsidiaries		1,415.7		1,458.3
Other assets		58.1		68.6
Total assets		3,972.4		3,937.2
Liabilities
Accounts payable		2.7		1.9
Accrued expenses and other liabilities		57.0		70.0
Total liabilities		1,277.8		1,284.5
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		2,694.6		2,652.7
Noncontrolling interests		0.0		0.0
Total equity		2,694.6		2,652.7
Total liabilities and equity		3,972.4		3,937.2
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | Mortgage Debt [Member]
Liabilities
Long-term debt		1,218.1		1,212.6
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | KW Unsecured Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member] | KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		247.0		384.2
Accounts receivable		34.8		51.4
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		3,298.6		3,831.9
Unconsolidated investments		586.6		407.3
Investments in and advances to consolidated subsidiaries		0.0		0.0
Other assets		246.2		205.3
Total assets		4,413.2		4,880.1
Liabilities
Accounts payable		13.7		21.5
Accrued expenses and other liabilities		229.4		217.6
Total liabilities		2,953.4		3,237.3
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,415.7		1,458.3
Noncontrolling interests		44.1		184.5
Total equity		1,459.8		1,642.8
Total liabilities and equity		4,413.2		4,880.1
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | Mortgage Debt [Member]
Liabilities
Long-term debt		1,457.2		1,737.7
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | KW Unsecured Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member] | KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		1,253.1		1,260.5
Elimination [Member]
Assets
Cash and cash equivalents		0.0		0.0
Accounts receivable		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		(5,386.9)		(5,387.9)
Other assets		0.0		0.0
Total assets		(5,386.9)		(5,387.9)
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		(5,386.9)		(5,387.9)
Noncontrolling interests		0.0		0.0
Total equity		(5,386.9)		(5,387.9)
Total liabilities and equity		(5,386.9)		(5,387.9)
Elimination [Member] | Mortgage Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Elimination [Member] | KW Unsecured Debt [Member]
Liabilities
Long-term debt		0.0		0.0
Elimination [Member] | KWE Unsecured Bonds [Member]
Liabilities
Long-term debt		$ 0.0		$ 0.0

[1] The assets and liabilities as of June 30, 2019 include $190.2 million (including cash held by consolidated investments of $10.8 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $170.6 million) and $138.6 million (including investment debt of $130.3 million), respectively, from consolidated variable interest entities ("VIEs"). The assets and liabilities as of December 31, 2018 include $657.8 million (including cash held by consolidated investments of $31.6 million and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $602.5 million) and $317.4 million (including investment debt of $283.6 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.