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 |
Total rabbi trust | 0.6 | 0.2 |
Total self-insured health plan trust | 7.6 | 8.8 |
Total Assets | 452 | 405 |
Liabilities | | |
Total | 0 | 0 |
Level 1 | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 0 | 0 |
Level 2 | | |
Assets | | |
Total nuclear decommissioning trust | 32.7 | 33.5 |
Total rabbi trust | 0 | 0 |
Total self-insured health plan trust | 5 | 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 |
Total rabbi trust | 0 | 0 |
Total self-insured health plan trust | 0 | 0 |
Total Assets | 0 | 0 |
Liabilities | | |
Total | 0 | 0 |
Level 3 | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 0 | 0 |
NAV | | |
Assets | | |
Total nuclear decommissioning trust | 41.8 | 42.6 |
Total rabbi trust | 44 | 43.6 |
Total self-insured health plan trust | 0 | 0 |
Total Assets | 85.8 | 86.2 |
Liabilities | | |
Total | 0 | 0 |
NAV | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 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 | 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 |
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 |
Westar Energy | Level 1 | Alternative investments fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 1 | Real estate securities fund | | |
Assets | | |
Total nuclear decommissioning trust | 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 |
Total rabbi trust | 0 | 0 |
Total Assets | 0 | 0 |
Westar Energy | Level 2 | Core bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Westar Energy | Level 2 | High-yield bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 2 | Emerging markets bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 2 | Combination debt/equity/other fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Westar Energy | Level 2 | Alternative investments fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 2 | Real estate securities fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 2 | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Westar Energy | Level 3 | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Total Assets | 0 | 0 |
Westar Energy | Level 3 | Core bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Westar Energy | Level 3 | High-yield bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 3 | Emerging markets bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 3 | Combination debt/equity/other fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 0 | 0 |
Westar Energy | Level 3 | Alternative investments fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 3 | Real estate securities fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | Level 3 | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 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 |
Westar Energy | NAV | Core bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 24.7 | 24.8 |
Westar Energy | NAV | High-yield bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | NAV | Emerging markets bond fund | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | NAV | Combination debt/equity/other fund | | |
Assets | | |
Total nuclear decommissioning trust | 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 | 11.8 |
Westar Energy | NAV | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total rabbi trust | 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 |
Westar Energy | Domestic | Level 3 | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 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 |
Westar Energy | International | Level 3 | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Westar Energy | International | NAV | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 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 |
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 | 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 |
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 | 42.1 |
KCP&L | Level 1 | U.S. Agency | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 1 | State and local obligations | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 1 | Corporate bonds | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 1 | Foreign governments | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 1 | Other | | |
Assets | | |
Total nuclear decommissioning trust | 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 |
KCP&L | Level 1 | Other | | |
Assets | | |
Total self-insured health plan trust | 0 | |
KCP&L | Level 2 | | |
Assets | | |
Total nuclear decommissioning trust | 32.7 | 33.5 |
Total self-insured health plan trust | 5 | 3.6 |
Total Assets | 37.7 | 37.1 |
KCP&L | Level 2 | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total self-insured health plan trust | 0 | 0 |
KCP&L | Level 2 | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 2 | U.S. Treasury | | |
Assets | | |
Total nuclear decommissioning trust | 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 |
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 |
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 |
Total self-insured health plan trust | 0 | 0 |
Total Assets | 0 | 0 |
KCP&L | Level 3 | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total self-insured health plan trust | 0 | 0 |
KCP&L | Level 3 | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | U.S. Treasury | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | U.S. Agency | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | State and local obligations | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | Corporate bonds | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | Foreign governments | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | Other | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | Level 3 | Debt securities | | |
Assets | | |
Total self-insured health plan trust | 0 | 0 |
KCP&L | Level 3 | Cash and cash equivalents | | |
Assets | | |
Total self-insured health plan trust | 0 | 0 |
KCP&L | Level 3 | Other | | |
Assets | | |
Total self-insured health plan trust | 0 | |
KCP&L | NAV | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total self-insured health plan trust | 0 | 0 |
Total Assets | 0 | 0 |
KCP&L | NAV | Equity securities | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
Total self-insured health plan trust | 0 | 0 |
KCP&L | NAV | Cash equivalents | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | U.S. Treasury | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | U.S. Agency | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | State and local obligations | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | Corporate bonds | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | Foreign governments | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | Other | | |
Assets | | |
Total nuclear decommissioning trust | 0 | 0 |
KCP&L | NAV | Debt securities | | |
Assets | | |
Total self-insured health plan trust | 0 | 0 |
KCP&L | NAV | Cash and cash equivalents | | |
Assets | | |
Total self-insured health plan trust | 0 | 0 |
KCP&L | NAV | Other | | |
Assets | | |
Total self-insured health plan trust | 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 |
Liabilities | | |
Total | 0 | 0 |
Other Evergy | Level 1 | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 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 |
Other Evergy | Level 2 | | |
Assets | | |
Total rabbi trust | 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 | |
Other Evergy | Level 2 | Fixed income fund | | |
Assets | | |
Total rabbi trust | 0 | 0 |
Other Evergy | Level 3 | | |
Assets | | |
Total rabbi trust | 0 | 0 |
Liabilities | | |
Total | 0 | 0 |
Other Evergy | Level 3 | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 0 | 0 |
Other Evergy | Level 3 | Cash and cash equivalents | | |
Assets | | |
Total rabbi trust | 0 | |
Other Evergy | Level 3 | Fixed income fund | | |
Assets | | |
Total rabbi trust | 0 | 0 |
Other Evergy | NAV | | |
Assets | | |
Total rabbi trust | 13.1 | 13.2 |
Liabilities | | |
Total | 0 | 0 |
Other Evergy | NAV | Interest rate swaps | | |
Liabilities | | |
Interest rate swaps | 0 | 0 |
Other Evergy | NAV | Cash and cash equivalents | | |
Assets | | |
Total rabbi trust | 0 | |
Other Evergy | NAV | Fixed income fund | | |
Assets | | |
Total rabbi trust | $ 13.1 | $ 13.2 |