Benefit Plans and Other Postretirement Benefits, Projected Benefit Payments (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Defined Contribution Plan, Administrative Expense		$ 2	$ 2	$ 2
Pension Plan [Member]
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2021		13
2022		12
2023		12
2024		12
2025		12
2026-2030		57
Pension Plan [Member] | NSP Wisconsin [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits		7	7	10
Pension Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits		150	154	150
Pension Plan [Member] | Subsequent Event
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits	$ 125
Pension Plan [Member] | Subsequent Event | NSP Wisconsin [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits	5
Pension Plan [Member] | Subsequent Event | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2021		1
2022		1
2023		1
2024		1
2025		1
2026-2030		3
Expected Medicare Part D Subsidies [Abstract]
2021		0
2022		0
2023		0
2024		0
2025		0
2026-2030		0
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
2021		1
2022		1
2023		1
2024		1
2025		1
2026-2030		3
Defined Benefit Plan, Overfunded Plan [Member] | NSP Wisconsin [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits		1	1
Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits		$ 11	$ 15	$ 11
Defined Benefit Plan, Overfunded Plan [Member] | Subsequent Event | NSP Wisconsin [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits	1
Defined Benefit Plan, Overfunded Plan [Member] | Subsequent Event | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits	$ 10