Commitments and Contingencies, Leases (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($) Lease	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Capital Leases [Abstract]
Number of leases qualifying as capital leases | Lease		3
Amortization expense under capital lease assets		$ 5	$ 8	$ 8
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease		222	222
Accumulated depreciation		(71)	(66)
Total property held under capital leases, net		151	156
Capital Leases, Future Minimum Payments Due [Abstract]
2018		15
2019		14
2020		14
2021		14
2022		12
Thereafter		233
Total minimum obligation		302
Interest component of obligation		(213)
Present value of minimum obligation	[1]	$ 89
Operating Leased Assets [Line Items]
Operating Lease Purchase Power Agreement Expiration Date		2039
Operating Leases, Future Minimum Payments Due [Abstract]
2018		$ 238
2019		260
2020		268
2021		270
2022		257
Thereafter		$ 1,830
WYCO Totem Gas Storage Facilities
Capital Leases [Abstract]
Ownership interest in joint venture (in hundredths)		50.00%
Capital Lease Obligations		$ 124	127
Percentage of the capital lease obligation related to WYCO eliminated (in hundredths)		50.00%
Gas Storage Facilities
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease		$ 201	201
Gas Pipeline
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease		21	21
Office Space and Other Equipment
Operating Leases [Abstract]
Total expenses under operating lease obligations		246	255	265
Operating Leases, Future Minimum Payments Due [Abstract]
2018		25
2019		30
2020		24
2021		24
2022		22
Thereafter		148
Purchased Power Agreements
Operating Leases [Abstract]
Payments for capacity for PPAs under operating lease obligations		210	$ 216	$ 224
Operating Leases, Future Minimum Payments Due [Abstract]
2018	[2],[3]	213
2019	[2],[3]	230
2020	[2],[3]	244
2021	[2],[3]	246
2022	[2],[3]	235
Thereafter	[2],[3]	$ 1,682

[1] Future commitments exclude certain amounts related to Xcel Energy’s 50 percent ownership interest in WYCO.

[2] Amounts do not include PPAs accounted for as executory contracts.

[3] PPA operating leases contractually expire through 2039.