Selected Balance Sheet Data (Tables)

3 Months Ended

Mar. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Thousands of Dollars)	March 31, 2018			Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$	332,506		$	314,009
Less allowance for bad debts	(19,980		)	(19,606		)
	$	312,526		$	294,403

Inventories

(Thousands of Dollars)	March 31, 2018		Dec. 31, 2017
Inventories
Materials and supplies	$	69,378	$	68,940
Fuel	53,282		73,893
Natural gas	31,266		71,656
	$	153,926	$	214,489

Property, Plant and Equipment, Net

(Thousands of Dollars)	March 31, 2018			Dec. 31, 2017
Property, plant and equipment, net
Electric plant	$	12,692,880		$	12,627,592
Natural gas plant	4,140,582			4,102,075
Common and other property	1,031,570			1,022,333
Plant to be retired (a)	10,627			10,949
Construction work in progress	1,264,835			1,014,338
Total property, plant and equipment	19,140,494			18,777,287
Less accumulated depreciation	(4,849,019		)	(4,751,536		)
	$	14,291,475		$	14,025,751

^(a)  In the third quarter of 2017, PSCo early retired Valmont Unit 5 and converted Cherokee Unit 4 from a coal-fueled generating facility to natural gas. PSCo also expects Craig Unit 1 to be early retired in approximately 2025. Amounts are presented net of accumulated depreciation.