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ORGANIZATION AND BASIS OF PRESENTATION - Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Restricted cash	$ 414.3	$ 0.0	$ 0.1	$ 0.1
KCP&L
Debt Instrument [Line Items]
Restricted cash	414.3	$ 0.0	$ 0.0	$ 0.0
KCP&L \| Senior Notes Due 2049 KCPL \| Senior Notest
Debt Instrument [Line Items]
Long-term debt gross	$ 400.0
Interest rates (in hundredths)	4.125%
KCP&L \| Senior Notes Due 2019 KCPL \| Senior Notest
Debt Instrument [Line Items]
Interest rates (in hundredths)	7.15%