Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2014

Commitments and Contingencies Disclosure [Abstract]

Estimated Minimum Purchases Under Fuel Contracts [Abstract]

The estimated minimum purchases for PSCo under these contracts as of Dec. 31, 2014, are as follows:

(Millions of Dollars)	Coal		Natural gas supply		Natural gas storage and transportation
2015	$	321.0	$	298.3	$	136.3
2016	261.3		153.0		79.6
2017	193.6		158.8		54.8
2018	42.4		212.3		53.9
2019	43.2		221.7		51.8
Thereafter	384.0		732.7		831.1
Total	$	1,245.5	$	1,776.8	$	1,207.5

Schedule of Long-term Contracts for Purchase of Electric Power [Table Text Block]

Included in electric fuel and purchased power expenses for PPAs, accounted for as executory contracts, were payments for capacity of $69.5 million, $72.7 million and $119.5 million in 2014, 2013 and 2012, respectively. At Dec. 31, 2014, the estimated future payments for capacity and energy that PSCo is obligated to purchase pursuant to these executory contracts, subject to availability, are as follows:

(Millions of Dollars)	Capacity		Energy (a)
2015	$	82.9	$	49.5
2016	58.4		22.5
2017	35.0		4.0
2018	27.8		—
2019	19.0		—
Thereafter	47.6		—
Total	$	270.7	$	76.0

^(a)  Excludes contingent energy payments for renewable energy PPAs.

Schedule of Capital Leased Assets [Table Text Block]

PSCo records amortization for its capital leases as cost of natural gas sold and transported on the consolidated statements of income. Total amortization expenses under capital lease assets were approximately $7.2 million, $6.3 million, and $5.7 million for 2014, 2013 and 2012, respectively. Following is a summary of property held under capital leases:

(Millions of Dollars)	Dec. 31, 2014			Dec. 31, 2013
Gas storage facilities	$	200.5		$	200.5
Gas pipeline	20.7			20.7
Property held under capital leases	221.2			221.2
Accumulated depreciation	(49.0		)	(41.8		)
Total property held under capital leases, net	$	172.2		$	179.4

Schedule Of Future Minimum Rental Payments For Operating And Capital Leases [Table Text Block]

Included in the future commitments under operating leases are estimated future capacity payments under PPAs that have been accounted for as operating leases in accordance with the applicable accounting guidance. Future commitments under operating and capital leases are:

(Millions of Dollars)	Operating Leases		PPA (a) (b) Operating Leases		Total Operating Leases		Capital Leases
2015	$	14.5	$	113.8	$	128.3	$	30.5
2016	11.7		102.8		114.5		29.3
2017	7.0		96.5		103.5		25.6
2018	6.7		96.7		103.4		25.3
2019	6.6		97.6		104.2		25.1
Thereafter	41.8		688.0		729.8		511.5
Total minimum obligation							647.3
Interest component of obligation							(475.1		)
Present value of minimum obligation							$	172.2

^(a)  Amounts do not include PPAs accounted for as executory contracts.

^(b)  PPA operating leases contractually expire through 2032.

Schedule of Asset Retirement Obligations [Table Text Block]

A reconciliation of PSCo’s AROs for the years ended Dec. 31, 2014 and 2013 is as follows:

(Thousands of Dollars)	Beginning Balance Jan. 1, 2014		Liabilities Recognized		Accretion		Cash Flow Revisions			Ending Balance  Dec. 31, 2014 (a)
Electric plant
Steam and other production asbestos	$	23,914	$	747	$	1,597	$	10,598		$	36,856
Steam and other production ash containment	29,234		—		1,897		30,754			61,885
Wind production	2,953		—		22		(880		)	2,095
Electric distribution	1,176		—		43		(37		)	1,182
Other	1,017		—		41		92			1,150
Natural gas plant
Gas transmission and distribution	788		18,252		50		98,384			117,474
Other	575		2,865		24		422			3,886
Common and other property
Common miscellaneous	741		—		27		—			768
Total liability	$	60,398	$	21,864	$	3,701	$	139,333		$	225,296

^(a)  There were no ARO liabilities settled during the year ended Dec. 31, 2014.

(Thousands of Dollars)	Beginning Balance Jan. 1, 2013		Liabilities Recognized		Liabilities Settled			Accretion		Cash Flow Revisions			Ending Balance Dec. 31, 2013
Electric plant
Steam and other production asbestos	$	19,734	$	—	$	(941	)	$	1,247	$	3,874		$	23,914
Steam and other production ash containment	12,919		—		—			684		15,631			29,234
Wind production	2,928		—		—			25		—			2,953
Electric distribution	6,392		—		—			178		(5,394		)	1,176
Other	627		—		—			60		330			1,017
Natural gas plant
Gas transmission and distribution	842		—		—			53		(107		)	788
Other	—		575		—			—		—			575
Common and other property
Common miscellaneous	309		—		—			29		403			741
Total liability	$	43,751	$	575	$	(941	)	$	2,276	$	14,737		$	60,398