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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 |

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