Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Pension Benefits [Abstract]
Total benefit obligation	$ 515,879	$ 483,601	$ 467,394
Net benefit cost recognized for financial reporting	$ 14,872	$ 17,446	$ 20,303
Expected average long-term rate of return on assets (as a percent)	6.78%	6.78%	7.22%
Expected average long-term rate of return on assets for next fiscal year (as a percent)	6.78%
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	100.00%	100.00%
Pension Plan [Member] | Domestic and international equity securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	34.00%	36.00%
Pension Plan [Member] | Long-duration fixed income and interest rate swap securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	31.00%	31.00%
Pension Plan [Member] | Short-to-intermediate fixed income securities
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	19.00%	15.00%
Pension Plan [Member] | Alternative investments
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	14.00%	16.00%
Pension Plan [Member] | Cash
Target Pension Asset Allocations [Abstract]
Target pension asset allocations (as a percent)	2.00%	2.00%
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Pension Benefits [Abstract]
Total benefit obligation	$ 2,000	$ 3,000
Minimum number of years historical achieved weighted average annual returns used to determine investment return assumptions (in years)	20 years
Xcel Energy Inc. | Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Pension Benefits [Abstract]
Total benefit obligation	$ 37,000	44,000
Net benefit cost recognized for financial reporting	$ 5,000	$ 8,000