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Schedule I - Statements of Comprehensive Income (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Statements of comprehensive income |  |  |  |  |  |  |  |  |  |  |
Net income attributed to common shareholders | $ 205.0 | $ 233.2 | $ 231.0 | $ 390.1 | $ 432.6 | $ 215.4 | $ 199.1 | $ 356.6 | $ 1,059.3 | $ 1,203.7 | $ 939.0
Other comprehensive loss, net of tax |  |  |  |  |  |  |  |  | (5.5) | 0.0 | (1.7)
Comprehensive income attributed to common shareholders |  |  |  |  |  |  |  |  | 1,053.8 | 1,203.7 | 937.3
Cash flow hedges |  |  |  |  |  |  |  |  |  |  |
Other comprehensive (loss) income, net of tax |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment from adoption of ASU 2018-02 | 1.6 |  |  |  | 0.0 |  |  |  | 1.6 | 0.0 | 0.0
Derivatives accounted for as cash flow hedges |  |  |  |  |  |  |  |  |  |  |
Net derivative losses, net of tax |  |  |  |  |  |  |  |  | (2.1) | 0.0 | 0.0
Reclassification of net gains to net income, net of tax |  |  |  |  |  |  |  |  | (1.2) | (1.3) | (1.3)
Cash flow hedges, net |  |  |  |  |  |  |  |  | (1.7) | (1.3) | (1.3)
Defined benefit plans |  |  |  |  |  |  |  |  |  |  |
Other comprehensive (loss) income, net of tax |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment from adoption of ASU 2018-02 | (1.0) |  |  |  | 0.0 |  |  |  | (1.0) | 0.0 | 0.0
Defined benefit plans |  |  |  |  |  |  |  |  |  |  |
Pension and OPEB costs arising during the period, net of tax |  |  |  |  |  |  |  |  | (3.1) | 0.9 | (0.8)
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax |  |  |  |  |  |  |  |  | 0.3 | 0.4 | 0.4
Defined benefit plans, net |  |  |  |  |  |  |  |  | (3.8) | 1.3 | (0.4)
WEC Energy Group |  |  |  |  |  |  |  |  |  |  |
Statements of comprehensive income |  |  |  |  |  |  |  |  |  |  |
Net income attributed to common shareholders |  |  |  |  |  |  |  |  | 1,059.3 | 1,203.7 | 939.0
Other comprehensive (loss) income from subsidiaries, net of tax |  |  |  |  |  |  |  |  | (2.8) | 1.2 | 0.3
Other comprehensive loss, net of tax |  |  |  |  |  |  |  |  | (5.5) | 0.0 | (1.7)
Comprehensive income attributed to common shareholders |  |  |  |  |  |  |  |  | 1,053.8 | 1,203.7 | 937.3
WEC Energy Group | Cash flow hedges |  |  |  |  |  |  |  |  |  |  |
Other comprehensive (loss) income, net of tax |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment from adoption of ASU 2018-02 | 1.6 |  |  |  | 0.0 |  |  |  | 1.6 | 0.0 | 0.0
Derivatives accounted for as cash flow hedges |  |  |  |  |  |  |  |  |  |  |
Net derivative losses, net of tax |  |  |  |  |  |  |  |  | (2.1) | 0.0 | 0.0
Reclassification of net gains to net income, net of tax |  |  |  |  |  |  |  |  | (1.2) | (1.3) | (1.3)
Cash flow hedges, net |  |  |  |  |  |  |  |  | (1.7) | (1.3) | (1.3)
WEC Energy Group | Defined benefit plans |  |  |  |  |  |  |  |  |  |  |
Other comprehensive (loss) income, net of tax |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment from adoption of ASU 2018-02 | $ (0.3) |  |  |  | $ 0.0 |  |  |  | (0.3) | 0.0 | 0.0
Defined benefit plans |  |  |  |  |  |  |  |  |  |  |
Pension and OPEB costs arising during the period, net of tax |  |  |  |  |  |  |  |  | (0.9) | (0.1) | (1.0)
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax |  |  |  |  |  |  |  |  | 0.2 | 0.2 | 0.3
Defined benefit plans, net |  |  |  |  |  |  |  |  | $ (1.0) | $ 0.1 | $ (0.7)

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