Summary of Significant Accounting Policies Inventory (Tables)

12 Months Ended

Dec. 31, 2020

Balance Sheet Related Disclosure - Inventory [Abstract]

Schedule of Utility Inventory [Table Text Block]

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

(Millions of Dollars)	Dec. 31, 2020		Dec. 31, 2019
Inventories
Materials and supplies	$	27	$	25
Fuel	9		6
Total inventories	$	36	$	31