Taxes Tax Credit Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 333.8
Tax Credit Carryforwards Originating In 2000	7.3
Tax Credit Carryforwards Originating In 2001	9.8
Tax Credit Carryforwards Originating In 2002	0.3
Tax Credit Carryforwards Originating In 2003	0.3
Tax Credit Carryforwards Originating In 2004	0.3
Tax Credit Carryforwards Originating In 2005	0.3
Tax Credit Carryforwards Originating In 2006	0.3
Tax Credit Carryforwards Originating In 2007	0.6
Tax Credit Carryforwards Originating In 2008	39.8
Tax Credit Carryforwards Originating In 2009	47.7
Tax Credit Carryforwards Originating In 2010	18.3
Tax Credit Carryforwards Originating In 2011	13.3
Tax Credit Carryforwards Originating In 2012	13.7
Tax Credit Carryforwards Originating In 2013	23.5
Tax Credit Carryforwards Originating In 2014	23.6
Tax Credit Carryforwards Originating In 2015	23.5
Tax Credit Carryforwards Originating In 2016	26.1
Tax Credit Carryforwards Originating In 2017	43.3
Tax Credit Carryforwards Originating In 2018	41.8
Westar Energy Inc [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	134.0
Tax Credit Carryforwards Originating In 2000	7.3
Tax Credit Carryforwards Originating In 2001	9.7
Tax Credit Carryforwards Originating In 2002	0.2
Tax Credit Carryforwards Originating In 2003	0.2
Tax Credit Carryforwards Originating In 2004	0.2
Tax Credit Carryforwards Originating In 2005	0.2
Tax Credit Carryforwards Originating In 2006	0.2
Tax Credit Carryforwards Originating In 2007	0.5
Tax Credit Carryforwards Originating In 2008	0.5
Tax Credit Carryforwards Originating In 2009	0.2
Tax Credit Carryforwards Originating In 2010	0.0
Tax Credit Carryforwards Originating In 2011	0.0
Tax Credit Carryforwards Originating In 2012	2.9
Tax Credit Carryforwards Originating In 2013	10.5
Tax Credit Carryforwards Originating In 2014	10.2
Tax Credit Carryforwards Originating In 2015	10.1
Tax Credit Carryforwards Originating In 2016	10.1
Tax Credit Carryforwards Originating In 2017	34.5
Tax Credit Carryforwards Originating In 2018	36.5
KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	192.8
Tax Credit Carryforwards Originating In 2000	0.0
Tax Credit Carryforwards Originating In 2001	0.0
Tax Credit Carryforwards Originating In 2002	0.0
Tax Credit Carryforwards Originating In 2003	0.0
Tax Credit Carryforwards Originating In 2004	0.0
Tax Credit Carryforwards Originating In 2005	0.0
Tax Credit Carryforwards Originating In 2006	0.0
Tax Credit Carryforwards Originating In 2007	0.0
Tax Credit Carryforwards Originating In 2008	38.9
Tax Credit Carryforwards Originating In 2009	47.4
Tax Credit Carryforwards Originating In 2010	18.2
Tax Credit Carryforwards Originating In 2011	13.2
Tax Credit Carryforwards Originating In 2012	10.7
Tax Credit Carryforwards Originating In 2013	12.9
Tax Credit Carryforwards Originating In 2014	13.0
Tax Credit Carryforwards Originating In 2015	12.8
Tax Credit Carryforwards Originating In 2016	12.4
Tax Credit Carryforwards Originating In 2017	8.2
Tax Credit Carryforwards Originating In 2018	5.1
General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	333.8	$ 100.0
Amount of tax credit acquired in business combination	0.5
Tax Credit Carryforward, Valuation Allowance	0.4
General Business Tax Credit Carryforward [Member] | Westar Energy Inc [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	134.0	100.0
General Business Tax Credit Carryforward [Member] | KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 192.8	184.6
General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2020
General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2038
Federal Alternative Minimum Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 73.4	52.2
Tax Credit Carryforward, Description	These credits do not expire and can be used to reduce taxes paid in the future or become refundable starting in 2018.
Tax Credit Carryforward, Valuation Allowance	$ 7.9
Federal Alternative Minimum Tax Credit Carryforward [Member] | Westar Energy Inc [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	26.7	52.2
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 174.3	176.7
Tax Credit Carryforward, Description	The state income tax credits relate primarily to the Kansas high performance incentive program tax credits and expire in the years 2024 to 2033.
State and Local Jurisdiction [Member] | Westar Energy Inc [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 173.1	176.7
State and Local Jurisdiction [Member] | KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 1.2	$ 1.2