Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Balance Sheet Related Disclosures [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	$	175.6	$	176.3
Fuel	103.2		88.5
Natural gas	26.0		34.6
Total inventories	$	304.8	$	299.4