Receivables - Summary of Bad Debt Expense (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment losses recognized on receivables	$ 4.5	$ 2.0	$ 10.6	$ 5.4
Westar Energy Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment losses recognized on receivables	1.1	2.0	6.2	5.4
KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment losses recognized on receivables	$ 3.9	$ 2.8	$ 7.5	$ 6.0