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Schedule I - Future Maturities of Long-Term Debt (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Future maturities of long-term debt outstanding |  |
2018 | $ 836.1 |
2020 | 684.4 |
Thereafter | 6,953.5 |
Total | 9,322.4 |
Long-term notes outstanding | 9,158.2 | $ 9,124.1
WECC |  |
Future maturities of long-term debt outstanding |  |
Long-term notes outstanding | 50.0 |
WEC Energy Group |  |
Future maturities of long-term debt outstanding |  |
2018 | 300.0 |
2020 | 400.0 |
Thereafter | 1,200.0 |
Total | 1,900.0 |
Long-term notes outstanding | $ 1,890.0 | $ 1,887.2

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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -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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