Selected Balance Sheet Data (Tables)

12 Months Ended

Dec. 31, 2016

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Thousands of Dollars)	Dec. 31, 2016			Dec. 31, 2015
Accounts receivable, net
Accounts receivable	$	827,112		$	776,494
Less allowance for bad debts	(50,823		)	(51,888		)
	$	776,289		$	724,606

Inventories

(Thousands of Dollars)	Dec. 31, 2016		Dec. 31, 2015
Inventories
Materials and supplies	$	312,430	$	290,690
Fuel	181,752		202,271
Natural gas	110,044		115,623
	$	604,226	$	608,584

Property, Plant and Equipment, Net

(Thousands of Dollars)	Dec. 31, 2016			Dec. 31, 2015
Property, plant and equipment, net
Electric plant	$	38,220,765		$	36,464,050
Natural gas plant	5,317,717			4,944,757
Common and other property	1,888,518			1,709,508
Plant to be retired (a)	31,839			38,249
CWIP	1,373,380			1,256,949
Total property, plant and equipment	46,832,219			44,413,513
Less accumulated depreciation	(14,381,603		)	(13,591,259		)
Nuclear fuel	2,571,770			2,447,251
Less accumulated amortization	(2,180,636		)	(2,063,654		)
	$	32,841,750		$	31,205,851

^(a)  In 2017, PSCo expects to early retire Valmont Unit 5 and convert 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.