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

12 Months Ended

Dec. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Public Utilities, Inventory

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

(Millions of Dollars)	Dec. 31, 2018		Dec. 31, 2017
Inventories
Materials and supplies	$	271	$	311
Fuel	170		186
Natural gas	107		113
	$	548	$	610