Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Estimated Minimum Purchases Under Fuel Contracts

Estimated minimum purchases under these contracts as of Dec. 31, 2018:

(Millions of Dollars)	Coal		Natural gas supply		Natural gas storage and transportation
2019	$	133.1	$	342.6	$	116.7
2020	86.4		261.6		115.1
2021	55.6		251.8		113.0
2022	32.5		113.0		113.1
2023	24.8		59.9		65.5
Thereafter	104.3		—		544.0
Total	$	436.7	$	1,028.9	$	1,067.4

Estimated Future Payments for Capacity and Energy Pursuant to Purchased Power Agreements

At Dec. 31, 2018, the estimated future payments for capacity that PSCo is obligated to purchase pursuant to these executory contracts, subject to availability, were as follows:

(Millions of Dollars)	Capacity
2019	$	12.3
2020	3.3
2021	3.2
2022	3.2
2023	3.2
Thereafter	9.8
Total	$	35.0

Summary of Property Held Under Capital Leases

Property held under capital leases:

(Millions of Dollars)	Dec. 31, 2018			Dec. 31, 2017
Gas storage facilities	$	200.5		$	200.5
Gas pipeline	20.7			20.7
Property held under capital leases	221.2			221.2
Accumulated depreciation	(76.2		)	(70.6		)
Total property held under capital leases, net	$	145.0		$	150.6

Future Commitments Under Operating and Capital Leases

Future commitments under operating and capital leases:

(Millions of Dollars)	Operating Leases		PPA (a) (b) Operating Leases		Total Operating Leases		Capital Leases
2019	$	10.8	$	95.5	$	106.3	$	24.9
2020	10.7		95.9		106.6		24.8
2021	9.5		96.4		105.9		23.6
2022	8.4		82.6		91.0		20.5
2023	8.1		70.0		78.1		20.3
Thereafter	53.4		288.6		342.0		420.4
Total minimum obligation							534.5
Interest component of obligation							(389.5		)
Present value of minimum obligation							$	145.0

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

^(b)  PPA operating leases contractually expire through 2034.

Asset Retirement Obligations

PSCo’s AROs were as follows:

	Dec. 31, 2018
(Millions  of Dollars)	Jan. 1, 2018		Amounts Incurred (a)		Amounts Settled (b)			Accretion		Cash Flow Revisions (c)			Dec. 31, 2018
Electric
Steam, hydro, and other production	$	103.2	$	—	$	(7.1	)	$	4.7	$	1.4		$	102.2
Wind	2.1		12.3		—			0.1		—			14.5
Distribution	7.9		—		—			0.3		5.2			13.4
Miscellaneous	1.4		—		(0.1		)	0.1		1.8			3.2
Natural gas
Transmission and distribution	228.9		—		—			9.3		(37.3		)	200.9
Miscellaneous	3.9		—		—			0.1		—			4.0
Common
Miscellaneous	0.4		—		—			0.1		—			0.5
Total liability	$	347.8	$	12.3	$	(7.2	)	$	14.7	$	(28.9	)	$	338.7

^(a)  Amounts incurred related to the Rush Creek wind farm, which was placed in service in 2018.

^(b)  Amounts settled related to closure of certain ash containment facilities.

^(c)  In 2018, AROs were revised for changes in timing and estimates of cash flows. Changes in gas transmission and distribution AROs were primarily related to increased gas line mileage and number of services, which were more than offset by increased discount rates. Changes in electric distribution AROs were primarily related to increased labor costs.

	Dec. 31, 2017
(Millions of  Dollars)	Jan. 1, 2017		Amounts Settled(a)			Accretion		Cash Flow Revisions (b)		Dec. 31, 2017 (c)
Electric
Steam, hydro, and other production	$	113.1	$	(24.1	)	$	5.1	$	9.1	$	103.2
Wind	2.1		—			—		—		2.1
Distribution	7.7		—			0.2		—		7.9
Miscellaneous	1.5		(0.2		)	0.1		—		1.4
Natural gas
Transmission and distribution	160.7		—			6.7		61.5		228.9
Miscellaneous	4.1		(0.4		)	0.2		—		3.9
Common
Miscellaneous	0.4		—			—		—		0.4
Total liability	$	289.6	$	(24.7	)	$	12.3	$	70.6	$	347.8

^(a)  Amounts settled related to asbestos abatement projects, closure of certain ash containment facilities, and removal and proper disposal of storage tanks and other above ground equipment.

^(b)  In 2017, AROs were revised for changes in timing and estimates of cash flows. Changes in gas transmission and distribution AROs were primarily related to increased labor costs.

^(c)  There were no ARO amounts incurred in 2017.

(Millions of Dollars)	2018		2017		2016
Total expense	$	110.6	$	108.6	$	118.2
Capacity payments	96.6		96.1		102.4

Total expense for energy and capacity payments table text block [Table Text Block]

Total expenses (including capacity payments) under operating lease obligations for PSCo and the corresponding capacity payments for PPAs accounted for as operating leases for the year ended Dec. 31:

(Millions of Dollars)	2018		2017		2016
Total expense	$	110.6	$	108.6	$	118.2
Capacity payments	96.6		96.1		102.4