XML 51 R37.htm IDEA: XBRL DOCUMENT v3.10.0.1
Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Supplemental Cash Flow Information [Abstract]    
Cash Paid for Interest – Net of Amounts Capitalized $ 33.0 $ 32.5
Noncash Investing and Financing Activities [Abstract]    
Decrease in Accounts Payable for Capital Additions to Property, Plant and Equipment (39.4) (0.4)
Reclassification of Property, Plant and Equipment to Inventory [1] 46.3 0.0
Capitalized Asset Retirement Costs 20.8 19.7
AFUDC–Equity 0.5 0.4
ALLETE Common Stock Contributed to the Pension Plans $ 0.0 $ 13.5
[1] On February 28, 2018, Montana-Dakota Utilities exercised its option to purchase the Thunder Spirit II wind energy facility upon completion, resulting in a reclassification of the project costs from Property, Plant and Equipment – Net to Inventories – Net as ALLETE Clean Energy will not own the facility upon completion.