Commitments and Contingencies, Purchased Power Agreements (Details) - Independent Power Producing Entities - MW	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Purchased Power Agreements [Abstract]
Purchase Power Agreement Duration, Maximum	2033	2033
Generating capacity under long term purchased power agreements	3,698	3,698

The maximum duration of purchase power agreements currently under contract (year).

No definition available.

Name:	xel_PurchasePowerAgreementDurationMaximum
Namespace Prefix:	xel_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration