Guarantor and Non-Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents		$ 512.9	$ 260.2
Cash held by consolidated investments		719.8	625.5
Accounts receivable		86.6	71.3
Loan purchases and originations		85.4	87.7
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		6,320.8	5,814.2
Unconsolidated investments		507.8	555.6
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		303.3	244.6
Total assets	[1]	8,536.6	7,659.1
Liabilities
Accounts payable		20.4	11.2
Accrued expenses and other liabilities		493.0	412.1
Total liabilities	[1]	6,142.3	5,316.0
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,013.4	1,048.0
Noncontrolling interests		1,380.9	1,295.1
Total equity		2,394.3	2,343.1
Total liabilities and equity		8,536.6	7,659.1
Investment Debt [Member]
Liabilities
Long-term debt		4,340.8	3,956.1
Senior Notes [Member]
Liabilities
Long-term debt		938.1	936.6
Line of Credit [Member]
Liabilities
Long-term debt		350.0
Reportable Legal Entities [Member] | Parent [Member]
Assets
Cash and cash equivalents		0.0	0.0
Cash held by consolidated investments		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		1,032.9	1,063.8
Other assets		0.0	0.0
Total assets		1,032.9	1,063.8
Liabilities
Accounts payable		0.0	0.0
Accrued expenses and other liabilities		19.5	15.8
Total liabilities		19.5	15.8
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,013.4	1,048.0
Noncontrolling interests		0.0	0.0
Total equity		1,013.4	1,048.0
Total liabilities and equity		1,032.9	1,063.8
Reportable Legal Entities [Member] | Kennedy-Wilson, Inc. [Member]
Assets
Cash and cash equivalents		441.7	106.0
Cash held by consolidated investments		0.0	0.0
Accounts receivable		0.0	0.0
Loan purchases and originations		0.3	0.3
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		0.0	0.0
Unconsolidated investments		19.5	18.8
Investments in and advances to consolidated subsidiaries		1,936.5	2,073.2
Other assets		1.5	2.6
Total assets		2,399.5	2,200.9
Liabilities
Accounts payable		0.9	0.5
Accrued expenses and other liabilities		77.6	200.0
Total liabilities		1,366.6	1,137.1
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,032.9	1,063.8
Noncontrolling interests		0.0	0.0
Total equity		1,032.9	1,063.8
Total liabilities and equity		2,399.5	2,200.9
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		45.5	45.4
Cash held by consolidated investments		0.0	0.0
Accounts receivable		51.8	37.5
Loan purchases and originations		5.8	12.1
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		1,507.6	1,482.5
Unconsolidated investments		313.4	380.0
Investments in and advances to consolidated subsidiaries		1,134.3	1,171.6
Other assets		45.3	39.7
Total assets		3,103.7	3,168.8
Liabilities
Accounts payable		1.2	1.6
Accrued expenses and other liabilities		159.7	157.2
Total liabilities		1,167.2	1,095.6
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,936.5	2,073.2
Noncontrolling interests		0.0	0.0
Total equity		1,936.5	2,073.2
Total liabilities and equity		3,103.7	3,168.8
Reportable Legal Entities [Member] | Non-guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		25.7	108.8
Cash held by consolidated investments		719.8	625.5
Accounts receivable		34.8	33.8
Loan purchases and originations		79.3	75.3
Real estate and acquired in place lease values, net of accumulated depreciation and amortization		4,813.2	4,331.7
Unconsolidated investments		174.9	156.8
Investments in and advances to consolidated subsidiaries		0.0	0.0
Other assets		256.5	202.3
Total assets		6,104.2	5,534.2
Liabilities
Accounts payable		18.3	9.1
Accrued expenses and other liabilities		236.2	39.1
Total liabilities		3,589.0	3,067.5
Equity
Kennedy-Wilson Holdings, Inc. shareholders' equity		1,134.3	1,171.6
Noncontrolling interests		1,380.9	1,295.1
Total equity		2,515.2	2,466.7
Total liabilities and equity		6,104.2	5,534.2
Reportable Legal Entities [Member] | Investment Debt [Member] | Parent [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Investment Debt [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Investment Debt [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		1,006.3	936.8
Reportable Legal Entities [Member] | Investment Debt [Member] | Non-guarantor Subsidiaries [Member]
Liabilities
Long-term debt		3,334.5	3,019.3
Reportable Legal Entities [Member] | Senior Notes [Member] | Parent [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Senior Notes [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		938.1	936.6
Reportable Legal Entities [Member] | Senior Notes [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Senior Notes [Member] | Non-guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0	0.0
Reportable Legal Entities [Member] | Line of Credit [Member] | Parent [Member]
Liabilities
Long-term debt		0.0
Reportable Legal Entities [Member] | Line of Credit [Member] | Kennedy-Wilson, Inc. [Member]
Liabilities
Long-term debt		350.0
Reportable Legal Entities [Member] | Line of Credit [Member] | Guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0
Reportable Legal Entities [Member] | Line of Credit [Member] | Non-guarantor Subsidiaries [Member]
Liabilities
Long-term debt		0.0
Elimination [Member]
Assets
Cash and cash equivalents		0.0	0.0
Cash held by consolidated investments		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		(4,103.7)	(4,308.6)
Other assets		0.0	0.0
Total assets		(4,103.7)	(4,308.6)
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		(4,103.7)	(4,308.6)
Noncontrolling interests		0.0	0.0
Total equity		(4,103.7)	(4,308.6)
Total liabilities and equity		(4,103.7)	(4,308.6)
Elimination [Member] | Investment Debt [Member]
Liabilities
Long-term debt		0.0	0.0
Elimination [Member] | Senior Notes [Member]
Liabilities
Long-term debt		0.0	$ 0.0
Elimination [Member] | Line of Credit [Member]
Liabilities
Long-term debt		$ 0.0

[1] The assets and liabilities as of September 30, 2017 include $4.9 billion (including cash held by consolidated investments of $0.7 billion and real estate and acquired in place lease values, net of accumulated depreciation and amortization of $3.9 billion) and $3.0 billion (including investment debt of $2.7 billion), 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 $0.6 billion 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.