KWE Unsecured Bonds - Schedule of KWE Unsecured Bonds (Details) - KWE Unsecured Bonds [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total debt	$ 1,284.7	$ 1,274.2
KWE [Member]
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	1,287.4	1,277.6
Unamortized loan fees	(2.7)	(3.4)
Total debt	1,284.7	1,274.2
Unamortized discount (premium)	(2.8)	(3.1)
KWE [Member] \| KWE Bonds [Member]
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	645.4	662.9
KWE [Member] \| KWE Euro Medium Term Note Programme [Member]
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	$ 642.0	$ 614.7

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