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ORGANIZATION AND BASIS OF PRESENTATION - Organization (Details) shares in Millions, customer in Millions		3 Months Ended
	Jun. 04, 2018 shares	Mar. 31, 2019 subsidiary customer segment MW
Summary Of Accounting Policies [Line Items]
Number of segments \| segment		1
Owned generating capacity and renewable purchased power \| MW		14,500
Number of customers served \| customer		1.6
Kansas Gas And Electric Company \| Westar Energy
Summary Of Accounting Policies [Line Items]
Number of active wholly owned subsidiaries \| subsidiary		1
Transource Energy, LLC \| GPE Transmission Holding Company, LLC
Summary Of Accounting Policies [Line Items]
Ownership percentage		13.50%
Transource Energy, LLC \| AEP Transmission Holding Company, LLC
Summary Of Accounting Policies [Line Items]
Ownership interest		86.50%
Prairie Wind Transmission, LLC \| Westar Energy
Summary Of Accounting Policies [Line Items]
Ownership percentage		50.00%
Great Plains Energy
Summary Of Accounting Policies [Line Items]
Conversion ratio	0.5981
Number of shares issued (in shares) \| shares	128.9
Westar Energy
Summary Of Accounting Policies [Line Items]
Conversion ratio	1