Summary of Significant Accounting Policies Inventory (Tables)

12 Months Ended

Dec. 31, 2019

Balance Sheet Related Disclosure - Inventory [Abstract]

Schedule of Utility Inventory [Table Text Block]

Inventory is recorded at average cost and consisted of the following:

(Millions of Dollars)	Dec. 31, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	24.7	$	25.7
Fuel	6.3		8.2
Total inventories	$	31.0	$	33.9