Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

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

Total expenses (including capacity payments) under operating lease obligations for SPS 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	$	59.0	$	57.8	$	56.6
Capacity payments	51.1		51.4		50.6

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	$	127.3	$	20.3	$	30.3
2020	83.9		—		30.3
2021	41.0		—		25.2
2022	41.2		—		19.3
2023	—		—		14.1
Thereafter	—		—		33.6
Total	$	293.4	$	20.3	$	152.8

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

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

(Millions of Dollars)	Capacity
2019	$	20.3
2020	12.0
2021	12.2
2022	12.4
2023	12.6
Thereafter	5.7
Total	$	75.2

Future Commitments Under Operating Leases

Future commitments under operating leases are:

(Millions of Dollars)	Operating Leases		PPA (a) (b) Operating Leases		Total Operating Leases
2019	$	5.2	$	46.7	$	51.9
2020	5.2		46.2		51.4
2021	5.1		46.2		51.3
2022	5.1		46.2		51.3
2023	5.1		46.2		51.3
Thereafter	56.3		450.8		507.1

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

^(b)  PPA operating leases contractually expire through 2033.

Asset Retirement Obligations

SPS’ AROs were as follows:

	Dec. 31, 2018
(Millions  of Dollars)	Balance Jan. 1, 2018		Accretion		Cash Flow Revisions (a)		Balance Dec. 31, 2018 (b)
Electric
Steam production	$	20.3	$	1.2	$	0.5	$	22.0
Distribution	7.0		0.3		1.8		9.1
Other	1.2		0.1		—		1.3
Total liability	$	28.5	$	1.6	$	2.3	$	32.4

^(a)  In 2018, AROs were revised for changes in timing and estimates of cash flows. Changes in electric distribution AROs were primarily related to increased labor costs.

^(b)  There were no ARO amounts incurred or settled in 2018.

	Dec. 31, 2017
(Millions  of Dollars)	Balance Jan. 1, 2017		Accretion		Cash Flow Revisions (a)			Balance Dec. 31, 2017 (b)
Electric plant
Steam production	$	20.7	$	1.3	$	(1.7	)	$	20.3
Distribution	6.8		0.2		—			7.0
Other	1.2		—		—			1.2
Total liability	$	28.7	$	1.5	$	(1.7	)	$	28.5

^(a)  In 2017, an asbestos ARO was revised for changes in timing of estimated cash flows.

^(b)  There were no ARO amounts incurred or settled in 2018.