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FAIR VALUE MEASUREMENTS - Recurring (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Assets |  |
Total nuclear decommissioning trust | $ 518.3 | $ 472.1
Total rabbi trust | 44.6 | 43.8
Total self-insured health plan trust | 12.6 | 12.4
Total Assets | 575.5 | 528.3
Liabilities |  |
Total | 19.2 | 5.4
Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 19.2 | 5.4
Level 1 |  |
Assets |  |
Total nuclear decommissioning trust | 443.8 | 396.0
Total rabbi trust | 0.6 | 0.2
Total self-insured health plan trust | 7.6 | 8.8
Total Assets | 452.0 | 405.0
Liabilities |  |
Total | 0.0 | 0.0
Level 1 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
Level 2 |  |
Assets |  |
Total nuclear decommissioning trust | 32.7 | 33.5
Total rabbi trust | 0.0 | 0.0
Total self-insured health plan trust | 5.0 | 3.6
Total Assets | 37.7 | 37.1
Liabilities |  |
Total | 19.2 | 5.4
Level 2 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 19.2 | 5.4
Level 3 |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
Total Assets | 0.0 | 0.0
Liabilities |  |
Total | 0.0 | 0.0
Level 3 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
NAV |  |
Assets |  |
Total nuclear decommissioning trust | 41.8 | 42.6
Total rabbi trust | 44.0 | 43.6
Total self-insured health plan trust | 0.0 | 0.0
Total Assets | 85.8 | 86.2
Liabilities |  |
Total | 0.0 | 0.0
NAV | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
Westar Energy |  |
Assets |  |
Total nuclear decommissioning trust | 248.4 | 227.5
Total rabbi trust | 31.1 | 30.6
Total Assets | 279.5 | 258.1
Westar Energy | Core bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 34.6 | 37.5
Total rabbi trust | 24.7 | 24.8
Westar Energy | High-yield bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 20.6 | 18.9
Westar Energy | Emerging markets bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 16.4 | 15.4
Westar Energy | Combination debt/equity/other fund |  |
Assets |  |
Total nuclear decommissioning trust | 14.7 | 12.9
Total rabbi trust | 6.2 | 5.6
Westar Energy | Alternative investments fund |  |
Assets |  |
Total nuclear decommissioning trust | 23.3 | 24.1
Westar Energy | Real estate securities fund |  |
Assets |  |
Total nuclear decommissioning trust | 12.0 | 11.8
Westar Energy | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.2 | 0.1
Total rabbi trust | 0.2 | 0.2
Westar Energy | Level 1 |  |
Assets |  |
Total nuclear decommissioning trust | 206.6 | 184.9
Total rabbi trust | 0.2 | 0.2
Total Assets | 206.8 | 185.1
Westar Energy | Level 1 | Core bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 34.6 | 37.5
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 1 | High-yield bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 20.6 | 18.9
Westar Energy | Level 1 | Emerging markets bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 16.4 | 15.4
Westar Energy | Level 1 | Combination debt/equity/other fund |  |
Assets |  |
Total nuclear decommissioning trust | 14.7 | 12.9
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 1 | Alternative investments fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 1 | Real estate securities fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 1 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.2 | 0.1
Total rabbi trust | 0.2 | 0.2
Westar Energy | Level 2 |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Total Assets | 0.0 | 0.0
Westar Energy | Level 2 | Core bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 2 | High-yield bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 2 | Emerging markets bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 2 | Combination debt/equity/other fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 2 | Alternative investments fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 2 | Real estate securities fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 2 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 3 |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Total Assets | 0.0 | 0.0
Westar Energy | Level 3 | Core bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 3 | High-yield bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 3 | Emerging markets bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 3 | Combination debt/equity/other fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Level 3 | Alternative investments fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 3 | Real estate securities fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Level 3 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | NAV |  |
Assets |  |
Total nuclear decommissioning trust | 41.8 | 42.6
Total rabbi trust | 30.9 | 30.4
Total Assets | 72.7 | 73.0
Westar Energy | NAV | Core bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 24.7 | 24.8
Westar Energy | NAV | High-yield bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | NAV | Emerging markets bond fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | NAV | Combination debt/equity/other fund |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 6.2 | 5.6
Westar Energy | NAV | Alternative investments fund |  |
Assets |  |
Total nuclear decommissioning trust | 23.3 | 24.1
Westar Energy | NAV | Real estate securities fund |  |
Assets |  |
Total nuclear decommissioning trust | 12.0 | 11.8
Westar Energy | NAV | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 0.0 | 0.0
Westar Energy | Domestic | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 80.1 | 70.6
Westar Energy | Domestic | Level 1 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 73.6 | 63.9
Westar Energy | Domestic | Level 2 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Domestic | Level 3 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | Domestic | NAV | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 6.5 | 6.7
Westar Energy | International | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 46.5 | 36.2
Westar Energy | International | Level 1 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 46.5 | 36.2
Westar Energy | International | Level 2 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | International | Level 3 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Westar Energy | International | NAV | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L |  |
Assets |  |
Total nuclear decommissioning trust | 269.9 | 244.6
Total self-insured health plan trust | 12.6 | 12.4
Total Assets | 282.5 | 257.0
KCP&L | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 188.3 | 166.6
Total self-insured health plan trust | 0.5 | 0.5
KCP&L | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 2.9 | 1.7
KCP&L | U.S. Treasury |  |
Assets |  |
Total nuclear decommissioning trust | 46.0 | 42.1
KCP&L | U.S. Agency |  |
Assets |  |
Total nuclear decommissioning trust | 0.4 | 0.4
KCP&L | State and local obligations |  |
Assets |  |
Total nuclear decommissioning trust | 2.1 | 2.1
KCP&L | Corporate bonds |  |
Assets |  |
Total nuclear decommissioning trust | 30.6 | 30.9
KCP&L | Foreign governments |  |
Assets |  |
Total nuclear decommissioning trust | 0.1 | 0.1
KCP&L | Other |  |
Assets |  |
Total nuclear decommissioning trust | (0.5) | 0.7
KCP&L | Debt securities |  |
Assets |  |
Total self-insured health plan trust | 4.3 | 3.9
KCP&L | Cash and cash equivalents |  |
Assets |  |
Total self-insured health plan trust | 6.7 | 8.0
KCP&L | Other |  |
Assets |  |
Total self-insured health plan trust | 1.1 |
KCP&L | Level 1 |  |
Assets |  |
Total nuclear decommissioning trust | 237.2 | 211.1
Total self-insured health plan trust | 7.6 | 8.8
Total Assets | 244.8 | 219.9
KCP&L | Level 1 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 188.3 | 166.6
Total self-insured health plan trust | 0.5 | 0.5
KCP&L | Level 1 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 2.9 | 1.7
KCP&L | Level 1 | U.S. Treasury |  |
Assets |  |
Total nuclear decommissioning trust | 46.0 | 42.1
KCP&L | Level 1 | U.S. Agency |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 1 | State and local obligations |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 1 | Corporate bonds |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 1 | Foreign governments |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 1 | Other |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.7
KCP&L | Level 1 | Debt securities |  |
Assets |  |
Total self-insured health plan trust | 0.4 | 0.3
KCP&L | Level 1 | Cash and cash equivalents |  |
Assets |  |
Total self-insured health plan trust | 6.7 | 8.0
KCP&L | Level 1 | Other |  |
Assets |  |
Total self-insured health plan trust | 0.0 |
KCP&L | Level 2 |  |
Assets |  |
Total nuclear decommissioning trust | 32.7 | 33.5
Total self-insured health plan trust | 5.0 | 3.6
Total Assets | 37.7 | 37.1
KCP&L | Level 2 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | Level 2 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 2 | U.S. Treasury |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 2 | U.S. Agency |  |
Assets |  |
Total nuclear decommissioning trust | 0.4 | 0.4
KCP&L | Level 2 | State and local obligations |  |
Assets |  |
Total nuclear decommissioning trust | 2.1 | 2.1
KCP&L | Level 2 | Corporate bonds |  |
Assets |  |
Total nuclear decommissioning trust | 30.6 | 30.9
KCP&L | Level 2 | Foreign governments |  |
Assets |  |
Total nuclear decommissioning trust | 0.1 | 0.1
KCP&L | Level 2 | Other |  |
Assets |  |
Total nuclear decommissioning trust | (0.5) | 0.0
KCP&L | Level 2 | Debt securities |  |
Assets |  |
Total self-insured health plan trust | 3.9 | 3.6
KCP&L | Level 2 | Cash and cash equivalents |  |
Assets |  |
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | Level 2 | Other |  |
Assets |  |
Total self-insured health plan trust | 1.1 |
KCP&L | Level 3 |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
Total Assets | 0.0 | 0.0
KCP&L | Level 3 | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | Level 3 | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | U.S. Treasury |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | U.S. Agency |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | State and local obligations |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | Corporate bonds |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | Foreign governments |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | Other |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | Level 3 | Debt securities |  |
Assets |  |
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | Level 3 | Cash and cash equivalents |  |
Assets |  |
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | Level 3 | Other |  |
Assets |  |
Total self-insured health plan trust | 0.0 |
KCP&L | NAV |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
Total Assets | 0.0 | 0.0
KCP&L | NAV | Equity securities |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | NAV | Cash equivalents |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | U.S. Treasury |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | U.S. Agency |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | State and local obligations |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | Corporate bonds |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | Foreign governments |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | Other |  |
Assets |  |
Total nuclear decommissioning trust | 0.0 | 0.0
KCP&L | NAV | Debt securities |  |
Assets |  |
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | NAV | Cash and cash equivalents |  |
Assets |  |
Total self-insured health plan trust | 0.0 | 0.0
KCP&L | NAV | Other |  |
Assets |  |
Total self-insured health plan trust | 0.0 |
Other Evergy |  |
Assets |  |
Total rabbi trust | 13.5 | 13.2
Liabilities |  |
Total | 19.2 | 5.4
Other Evergy | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 19.2 | 5.4
Other Evergy | Cash and cash equivalents |  |
Assets |  |
Total rabbi trust | 0.4 |
Other Evergy | Fixed income fund |  |
Assets |  |
Total rabbi trust | 13.1 | 13.2
Other Evergy | Level 1 |  |
Assets |  |
Total rabbi trust | 0.4 | 0.0
Liabilities |  |
Total | 0.0 | 0.0
Other Evergy | Level 1 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
Other Evergy | Level 1 | Cash and cash equivalents |  |
Assets |  |
Total rabbi trust | 0.4 |
Other Evergy | Level 1 | Fixed income fund |  |
Assets |  |
Total rabbi trust | 0.0 | 0.0
Other Evergy | Level 2 |  |
Assets |  |
Total rabbi trust | 0.0 | 0.0
Liabilities |  |
Total | 19.2 | 5.4
Other Evergy | Level 2 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 19.2 | 5.4
Other Evergy | Level 2 | Cash and cash equivalents |  |
Assets |  |
Total rabbi trust | 0.0 |
Other Evergy | Level 2 | Fixed income fund |  |
Assets |  |
Total rabbi trust | 0.0 | 0.0
Other Evergy | Level 3 |  |
Assets |  |
Total rabbi trust | 0.0 | 0.0
Liabilities |  |
Total | 0.0 | 0.0
Other Evergy | Level 3 | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
Other Evergy | Level 3 | Cash and cash equivalents |  |
Assets |  |
Total rabbi trust | 0.0 |
Other Evergy | Level 3 | Fixed income fund |  |
Assets |  |
Total rabbi trust | 0.0 | 0.0
Other Evergy | NAV |  |
Assets |  |
Total rabbi trust | 13.1 | 13.2
Liabilities |  |
Total | 0.0 | 0.0
Other Evergy | NAV | Interest rate swaps |  |
Liabilities |  |
Interest rate swaps | 0.0 | 0.0
Other Evergy | NAV | Cash and cash equivalents |  |
Assets |  |
Total rabbi trust | 0.0 |
Other Evergy | NAV | Fixed income fund |  |
Assets |  |
Total rabbi trust | $ 13.1 | $ 13.2

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- Definition The fair value of investments held in a trust for KCP&L's self-insurance health plan. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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