Taxes Net Operating Loss Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Valuation Allowance	$ 7.1
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	324.2	$ 38.0
Amount of Net Operating Losses related to business acquisition	78.1
Net operating losses year of origination [Abstract]
Net operating loss carryfowards originating in 2004	1.6
Net operating loss carryfowards originating in 2005	44.4
Net operating loss carryfowards originating in 2006	32.0
Net operating loss carryfowards originating in 2009	21.9
Net operating loss carryfowards originating in 2010	2.5
Net operating loss carryfowards originating in 2011	65.3
Net operating loss carryforwards originating in 2012	0.2
Net operating loss carryforwards originating in 2013	1.5
Net operating loss carryforwards originating in 2014	77.2
Net operating loss carryforwards originating in 2015	59.3
Net operating loss carryforwards originating in 2016	0.8
Net operating loss carryforwards originating in 2017	16.2
Net operating loss carryforwards originating in 2018	$ 1.3
Internal Revenue Service (IRS) [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2022
Internal Revenue Service (IRS) [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 59.1	26.0
Operating Loss Carryforwards, Valuation Allowance	$ 11.9
State and Local Jurisdiction [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2019
State and Local Jurisdiction [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Westar Energy Inc [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 40.1	38.0
Net operating losses year of origination [Abstract]
Net operating loss carryfowards originating in 2004	0.0
Net operating loss carryfowards originating in 2005	0.0
Net operating loss carryfowards originating in 2006	0.0
Net operating loss carryfowards originating in 2009	0.0
Net operating loss carryfowards originating in 2010	0.0
Net operating loss carryfowards originating in 2011	0.0
Net operating loss carryforwards originating in 2012	0.2
Net operating loss carryforwards originating in 2013	0.8
Net operating loss carryforwards originating in 2014	25.0
Net operating loss carryforwards originating in 2015	0.2
Net operating loss carryforwards originating in 2016	0.4
Net operating loss carryforwards originating in 2017	12.3
Net operating loss carryforwards originating in 2018	1.2
Westar Energy Inc [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	20.6	26.0
KCPL [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	107.5	107.3
Net operating losses year of origination [Abstract]
Net operating loss carryfowards originating in 2004	0.0
Net operating loss carryfowards originating in 2005	0.0
Net operating loss carryfowards originating in 2006	0.0
Net operating loss carryfowards originating in 2009	0.0
Net operating loss carryfowards originating in 2010	0.0
Net operating loss carryfowards originating in 2011	38.4
Net operating loss carryforwards originating in 2012	0.0
Net operating loss carryforwards originating in 2013	0.3
Net operating loss carryforwards originating in 2014	12.3
Net operating loss carryforwards originating in 2015	55.6
Net operating loss carryforwards originating in 2016	0.3
Net operating loss carryforwards originating in 2017	0.6
Net operating loss carryforwards originating in 2018	0.0
KCPL [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 11.7	$ 23.9