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Long-Term Debt and Capital Lease Obligations - Long-term Debt (Details) $ in Millions |  | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Oct. 15, 2018 USD ($) | Dec. 31, 2018 USD ($) | Nov. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | May 31, 2018 USD ($) | Dec. 31, 2018 USD ($) number_of_interest_rate_swaps | Jul. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | May 15, 2017
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Number of interest rate swaps executed | number_of_interest_rate_swaps |  |  |  |  |  | 2 |  |  |
Future maturities of long-term debt outstanding |  |  |  |  |  |  |  |  |
2019 |  | $ 360.1 |  |  |  | $ 360.1 |  |  |
2020 |  | 686.9 |  |  |  | 686.9 |  |  |
2021 |  | 1,338.8 |  |  |  | 1,338.8 |  |  |
2022 |  | 40.8 |  |  |  | 40.8 |  |  |
2023 |  | 42.8 |  |  |  | 42.8 |  |  |
Thereafter |  | 7,918.2 |  |  |  | 7,918.2 |  |  |
Total |  | 10,387.6 |  |  |  | 10,387.6 |  |  |
WEC Energy Group |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Current portion of long-term debt |  | 0.0 |  |  |  | 0.0 |  | $ 300.0 |
Future maturities of long-term debt outstanding |  |  |  |  |  |  |  |  |
2020 |  | 400.0 |  |  |  | 400.0 |  |  |
2021 |  | 600.0 |  |  |  | 600.0 |  |  |
Thereafter |  | 1,200.0 |  |  |  | 1,200.0 |  |  |
Total |  | 2,200.0 |  |  |  | 2,200.0 |  |  |
WEC Energy Group | WEC 2007 Junior Notes due 2067 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 500.0 |  |  |  | $ 500.0 |  | $ 500.0 |
Debt instrument interest rate stated percentage rate |  | 4.73% |  |  |  | 4.73% |  | 3.53% | 6.25%
WEC Energy Group | WEC 3.375% Senior Notes due June 15, 2021 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 600.0 |  |  |  | $ 600.0 |  | $ 0.0 |
Proceeds from issuance of debt |  |  |  | $ 600.0 |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 3.375% |  | 3.375% |  | 3.375% |  |  |
WEC Energy Group | WEC Senior Notes due 2018 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 0.0 |  |  |  | $ 0.0 |  | 300.0 |
Debt instrument interest rate stated percentage rate |  | 1.65% |  | 1.65% |  | 1.65% |  |  |
Extinguishment of debt |  |  |  | $ 300.0 |  |  |  |  |
WEC Energy Group | WEC Energy Group senior notes (unsecured), 6.20% due 2033 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 200.0 |  |  |  | $ 200.0 |  | 200.0 |
Debt instrument interest rate stated percentage rate |  | 6.20% |  |  |  | 6.20% |  |  |
WE |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term pollution control bond |  |  |  |  |  |  | $ 80.0 |  |
WE | WE 4.30% Debentures due 2048 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 300.0 |  |  |  | $ 300.0 |  | 0.0 |
Proceeds from issuance of debt | $ 300.0 |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate | 4.30% | 4.30% |  |  |  | 4.30% |  |  |
WE | WE Debentures due 2018 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 0.0 |  |  |  | $ 0.0 |  | 250.0 |
Debt instrument interest rate stated percentage rate |  | 1.70% |  | 1.70% |  | 1.70% |  |  |
Extinguishment of debt |  |  |  | $ 250.0 |  |  |  |  |
WPS | WPS Senior Notes due November 21, 2021 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 400.0 |  |  |  | $ 400.0 |  | 0.0 |
Proceeds from issuance of debt |  |  | $ 400.0 |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 3.35% | 3.35% |  |  | 3.35% |  |  |
WPS | WPS Senior Notes (unsecured), 1.65% due 2018 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 0.0 |  |  |  | $ 0.0 |  | 250.0 |
Debt instrument interest rate stated percentage rate |  | 1.65% |  |  |  | 1.65% |  |  |
Extinguishment of debt |  | $ 250.0 |  |  |  |  |  |  |
PGL | PGL Series FFF Bonds due 2028 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | $ 150.0 |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 3.87% | 3.87% |  |  | 3.87% |  |  |
PGL | PGL First and Refunding Mortgage Bonds (secured), 8.00% due 2018 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 8.00% | 8.00% |  |  | 8.00% |  |  |
Extinguishment of debt |  |  | $ 5.0 |  |  |  |  |  |
NSG | NSG Series R Bonds due 2028 [Member] |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | $ 50.0 |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 3.87% | 3.87% |  |  | 3.87% |  |  |
We Power | We Power Subsidiaries Notes (secured, nonrecourse), 4.91% due 2019-2030 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 4.91% |  |  |  | 4.91% |  |  |
Current portion of long-term debt |  | $ 6.2 |  |  |  | $ 6.2 |  |  |
Long-term debt, gross |  | $ 95.1 |  |  |  | $ 95.1 |  |  |
We Power | We Power Subsidiaries Notes (secured, nonrecourse), 6.00% due 2019-2033 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 6.00% |  |  |  | 6.00% |  |  |
Current portion of long-term debt |  | $ 5.2 |  |  |  | $ 5.2 |  |  |
Long-term debt, gross |  | $ 116.6 |  |  |  | $ 116.6 |  |  |
We Power | We Power Subsidiaries Notes (secured, nonrecourse), 5.209% due 2019-2030 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 5.209% |  |  |  | 5.209% |  |  |
Current portion of long-term debt |  | $ 12.0 |  |  |  | $ 12.0 |  |  |
Long-term debt, gross |  | $ 182.7 |  |  |  | $ 182.7 |  |  |
We Power | We Power Subsidiaries Notes (secured, nonrecourse), 4.673% due 2019-2031 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 4.673% |  |  |  | 4.673% |  |  |
Current portion of long-term debt |  | $ 9.3 |  |  |  | $ 9.3 |  |  |
Long-term debt, gross |  | 153.5 |  |  |  | 153.5 |  |  |
Integrys Holding Inc | Integrys 2006 Junior Notes due 2066 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 0.0 |  |  |  | $ 0.0 |  | 114.9 |
Debt instrument interest rate stated percentage rate |  | 3.60% |  |  |  | 3.60% |  |  |
Extinguishment of debt |  |  |  |  | $ 114.9 |  |  |  |
Integrys Holding Inc | Integrys junior notes (unsecured), 6.00% due 2073 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 400.0 |  |  |  | $ 400.0 |  | 400.0 |
Debt instrument interest rate stated percentage rate |  | 6.00% |  |  |  | 6.00% |  |  |
Debt instrument, basis spread on variable rate |  |  |  |  |  | 3.22% |  |  |
Long-term debt, gross |  | $ 400.0 |  |  |  | $ 400.0 |  |  |
Bluewater Gas Storage, LLC | Bluewater Gas Storage senior notes (unsecured), 3.76% due 2047 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 122.7 |  |  |  | $ 122.7 |  | 125.0 |
Debt instrument interest rate stated percentage rate |  | 3.76% |  |  |  | 3.76% |  |  |
Current portion of long-term debt |  | $ 2.4 |  |  |  | $ 2.4 |  |  |
Long-term debt, gross |  | 122.7 |  |  |  | 122.7 |  |  |
ATC Holding LLC | ATC Holding Total Senior Notes issued December 2018 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  | 240.0 |  |  |  |  |  |  |
ATC Holding LLC | ATC Holding 4.18% Senior Notes due December 20, 2025 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | 85.0 |  |  |  | $ 85.0 |  | 0.0 |
Proceeds from issuance of debt |  | $ 85.0 |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 4.18% |  |  |  | 4.18% |  |  |
ATC Holding LLC | ATC Holding 4.37% Senior Notes due December 20, 2028 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 56.5 |  |  |  | $ 56.5 |  | 0.0 |
Proceeds from issuance of debt |  | $ 56.5 |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 4.37% |  |  |  | 4.37% |  |  |
ATC Holding LLC | ATC Holding 4.47% Senior Notes due December 20, 2030 |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 98.5 |  |  |  | $ 98.5 |  | $ 0.0 |
Proceeds from issuance of debt |  | $ 98.5 |  |  |  |  |  |  |
Debt instrument interest rate stated percentage rate |  | 4.47% |  |  |  | 4.47% |  |  |
Interest rate swaps | WEC Energy Group |  |  |  |  |  |  |  |  |
Debt Disclosure [Abstract] |  |  |  |  |  |  |  |  |
Number of interest rate swaps executed | number_of_interest_rate_swaps |  |  |  |  |  | 2 |  |  |
Interest rate swap notional value |  | $ 250.0 |  |  |  | $ 250.0 | $ 250.0 |  |
Interest rate swap fixed interest rate |  | 4.9765% |  |  |  | 4.9765% |  |  |

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