Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income
Income (Loss) from Equity Method Investments									$ 39	$ 35	$ 30
Expenses and other deductions
Other income									(16)	14	10
Interest charges and financing costs									773	700	663
Income before income taxes									1,500	1,442	1,690
Income tax benefit									128	181	542
Net income	$ 292	$ 527	$ 238	$ 315	$ 214	$ 491	$ 265	$ 291	1,372	1,261	1,148
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Pension and retiree medical benefits, net of tax of $1, $1 and $3, respectively									0	(6)	(3)
Total comprehensive income									$ 1,355	$ 1,262	$ 1,155
Weighted average common shares outstanding:
Basic (in shares)									519	511	509
Diluted (in shares)									520	511	509
Earnings per average common share:
Basic (in dollars per share)	$ 0.56	$ 1.02	$ 0.46	$ 0.61	$ 0.42	$ 0.96	$ 0.52	$ 0.57	$ 2.64	$ 2.47	$ 2.26
Diluted (in dollars per share)	$ 0.56	$ 1.01	$ 0.46	$ 0.61	$ 0.42	$ 0.96	$ 0.52	$ 0.57	$ 2.64	$ 2.47	$ 2.25
Xcel Energy Inc.
Income
Income (Loss) from Equity Method Investments									$ 1,505	$ 1,393	$ 1,263
Total income									1,505	1,393	1,263
Expenses and other deductions
Operating expenses									23	24	30
Other income									(9)	(1)	(6)
Interest charges and financing costs									173	149	128
Total expenses and other deductions									187	172	152
Income before income taxes									1,318	1,221	1,111
Income tax benefit									(54)	(40)	(37)
Net income									1,372	1,261	1,148
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Pension and retiree medical benefits, net of tax of $1, $1 and $3, respectively									3	3	4
Derivative instruments, net of tax of $(7), $(1) and $2, respectively									(20)	(2)	3
Other Comprehensive Income (Loss), Net of Tax									(17)	1	7
Total comprehensive income									$ 1,355	$ 1,262	$ 1,155