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Schedule I - Statements of Cash Flows (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
Operating activities |  |  |  |  |  |  |  |  |  |  |
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
Reconciliation to cash provided by operating activities |  |  |  |  |  |  |  |  |  |  |
Equity income in subsidiaries, net of distributions |  |  |  |  |  |  |  |  | (18.6) | (4.8) | (46.6)
Deferred income taxes |  |  |  |  |  |  |  |  | 300.1 | 274.4 | 498.7
Change in - |  |  |  |  |  |  |  |  |  |  |
Other current assets |  |  |  |  |  |  |  |  | (10.0) | (7.1) | 103.2
Other current liabilities |  |  |  |  |  |  |  |  | (67.6) | 161.8 | (20.8)
Other, net |  |  |  |  |  |  |  |  | 290.4 | (197.4) | (53.6)
Net cash provided by operating activities |  |  |  |  |  |  |  |  |  | 2,078.6 | 2,103.8
Investing activities |  |  |  |  |  |  |  |  |  |  |
Acquisition of Bluewater |  |  |  |  |  |  |  |  | 0.0 | (226.0) | 0.0
Capital contributions to subsidiaries |  |  |  |  |  |  |  |  | (53.5) | (109.6) | (42.3)
Other, net |  |  |  |  |  |  |  |  | 20.5 | 12.0 | 3.0
Net cash used in investing activities |  |  |  |  |  |  |  |  |  | (2,254.1) | (1,354.2)
Financing activities |  |  |  |  |  |  |  |  |  |  |
Exercise of stock options |  |  |  |  |  |  |  |  | 29.1 | 30.8 | 41.6
Purchase of common stock |  |  |  |  |  |  |  |  | (72.4) | (71.3) | (108.0)
Dividends paid on common stock |  |  |  |  |  |  |  |  | (697.3) | (656.5) | (624.9)
Issuance of long-term debt |  |  |  |  |  |  |  |  | 1,740.0 | 435.0 | 400.0
Retirement of long-term debt |  |  |  |  |  |  |  |  | (953.3) | (154.5) | (306.0)
Other, net |  |  |  |  |  |  |  |  | (15.2) | (6.5) | (13.6)
Cash and cash equivalents at beginning of year |  |  |  | 38.9 |  |  |  | 37.5 | 38.9 | 37.5 |
Cash and cash equivalents at end of year | 84.5 |  |  |  | 38.9 |  |  |  | 84.5 | 38.9 | 37.5
WEC Energy Group |  |  |  |  |  |  |  |  |  |  |
Operating activities |  |  |  |  |  |  |  |  |  |  |
Net income attributed to common shareholders |  |  |  |  |  |  |  |  | 1,059.3 | 1,203.7 | 939.0
Reconciliation to cash provided by operating activities |  |  |  |  |  |  |  |  |  |  |
Equity income in subsidiaries, net of distributions |  |  |  |  |  |  |  |  | (419.4) | (686.1) | (271.1)
Deferred income taxes |  |  |  |  |  |  |  |  | 14.4 | 89.5 | 23.2
Change in - |  |  |  |  |  |  |  |  |  |  |
Prepaid taxes |  |  |  |  |  |  |  |  | 17.5 | 28.4 | (47.6)
Other current assets |  |  |  |  |  |  |  |  | (2.1) | (0.1) | 13.0
Accrued taxes |  |  |  |  |  |  |  |  | 3.6 | 0.0 | (75.6)
Other current liabilities |  |  |  |  |  |  |  |  | 5.7 | (1.9) | (5.6)
Other, net |  |  |  |  |  |  |  |  | 5.6 | 0.9 | 6.3
Net cash provided by operating activities |  |  |  |  |  |  |  |  | 684.6 | 634.4 | 581.6
Investing activities |  |  |  |  |  |  |  |  |  |  |
Acquisition of Bluewater |  |  |  |  |  |  |  |  | 0.0 | (226.0) | 0.0
Capital contributions to subsidiaries |  |  |  |  |  |  |  |  | (448.7) | (173.4) | (55.8)
Return of capital from subsidiaries |  |  |  |  |  |  |  |  | 290.2 | 0.0 | 9.0
Short-term notes receivable from related parties, net |  |  |  |  |  |  |  |  | (6.9) | 167.8 | 46.8
Issuance of long-term notes receivable to UMERC |  |  |  |  |  |  |  |  | (100.0) | (50.0) | 0.0
Purchase of subsidiary's common stock |  |  |  |  |  |  |  |  | 0.0 | 0.0 | (66.4)
Other, net |  |  |  |  |  |  |  |  | 6.4 | 4.5 | (0.4)
Net cash used in investing activities |  |  |  |  |  |  |  |  | (259.0) | (277.1) | (66.8)
Financing activities |  |  |  |  |  |  |  |  |  |  |
Exercise of stock options |  |  |  |  |  |  |  |  | 29.1 | 30.8 | 41.6
Purchase of common stock |  |  |  |  |  |  |  |  | (72.4) | (71.3) | (108.0)
Dividends paid on common stock |  |  |  |  |  |  |  |  | (697.3) | (656.5) | (624.9)
Issuance of long-term debt |  |  |  |  |  |  |  |  | 600.0 | 0.0 | 0.0
Retirement of long-term debt |  |  |  |  |  |  |  |  | (300.0) | 0.0 | 0.0
Change in short-term debt |  |  |  |  |  |  |  |  | 53.6 | 173.0 | 13.9
Short-term notes payable to related parties, net |  |  |  |  |  |  |  |  | (6.2) | 169.5 | 162.3
Other, net |  |  |  |  |  |  |  |  | (3.6) | 0.0 | 0.2
Net cash used in financing activities |  |  |  |  |  |  |  |  | (396.8) | (354.5) | (514.9)
Net change in cash and cash equivalents |  |  |  |  |  |  |  |  | 28.8 | 2.8 | (0.1)
Cash and cash equivalents at beginning of year |  |  |  | $ 4.0 |  |  |  | $ 1.2 | 4.0 | 1.2 | 1.3
Cash and cash equivalents at end of year | $ 32.8 |  |  |  | $ 4.0 |  |  |  | $ 32.8 | $ 4.0 | $ 1.2

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- Definition The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585 + Details
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- Definition Amount of cash inflow (outflow) from financing activities classified as other. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585 + Details
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- Definition The net cash inflow or outflow for borrowing having initial term of repayment within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109197908&loc=SL79508275-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585 + Details
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- Definition The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585 + Details
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