Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Funded Status of Plans at Dec. 31 [Abstract]
Noncurrent liabilities		$ (112,000,000)		$ (192,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
Plan Amendments		0
Pension Plan
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		989,000,000		942,000,000
Service cost		30,000,000		27,000,000		$ 25,000,000
Interest cost		25,000,000		31,000,000		37,000,000
Actuarial (gain) loss		(28,000,000)		84,000,000
Benefit payments		(140,000,000)		(95,000,000)
Obligation at Dec. 31		877,000,000		989,000,000		942,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		897,000,000	[1]	815,000,000
Actual return (loss) on plan assets		62,000,000		133,000,000
Employer contributions		34,000,000		44,000,000
Benefit payments		(140,000,000)		(95,000,000)
Fair value of plan assets at Dec. 31		853,000,000	[1]	897,000,000	[1]	815,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		(24,000,000)		(92,000,000)
Current liabilities		0		0
Noncurrent liabilities		(24,000,000)		(92,000,000)
Net postretirement amounts recognized on consolidated balance sheets		(24,000,000)		(92,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss		307,000,000		414,000,000
Prior service (credit) cost		0		0
Total		307,000,000		414,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Noncurrent regulatory assets		282,000,000		385,000,000
Deferred income taxes		0		0
Net-of-tax accumulated other comprehensive income		0		0
Total		$ 307,000,000		$ 414,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.08%		2.71%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 30,000,000		$ 27,000,000		25,000,000
Interest cost		25,000,000		31,000,000		37,000,000
Expected return on plan assets		(52,000,000)		(55,000,000)		(54,000,000)
Amortization of prior service cost (credit)		0		0		0
Amortization of net loss		34,000,000		33,000,000		30,000,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	35,000,000		0		0
Net periodic postretirement benefit cost		72,000,000		36,000,000		38,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Plan amendments		1,000,000		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		25,000,000		29,000,000
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation		(44,000,000)		(4,000,000)		(5,000,000)
Net benefit cost recognized for financial reporting		$ 28,000,000		$ 32,000,000		$ 33,000,000
Discount rate (as a percent)		2.71%		3.49%		4.31%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		3.75%		3.75%		3.75%
Expected average long-term rate of return on assets (as a percent)		6.60%		7.10%		7.10%
Postretirement Benefits Plan
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 73,000,000		$ 76,000,000
Service cost		0		0		$ 0
Interest cost		2,000,000		2,000,000		3,000,000
Actuarial (gain) loss		(5,000,000)		2,000,000
Benefit payments		(6,000,000)		(7,000,000)
Obligation at Dec. 31		64,000,000		73,000,000		76,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		2,000,000		3,000,000
Actual return (loss) on plan assets		0		0
Employer contributions		7,000,000		6,000,000
Benefit payments		(6,000,000)		(7,000,000)
Fair value of plan assets at Dec. 31		3,000,000	[3]	2,000,000		3,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		(61,000,000)		(71,000,000)
Current liabilities		(3,000,000)		(5,000,000)
Noncurrent liabilities		(58,000,000)		(66,000,000)
Net postretirement amounts recognized on consolidated balance sheets		(61,000,000)		(71,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss		31,000,000		37,000,000
Prior service (credit) cost		(4,000,000)		(6,000,000)
Total		27,000,000		31,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Noncurrent regulatory assets		25,000,000		29,000,000
Deferred income taxes		1,000,000		1,000,000
Net-of-tax accumulated other comprehensive income		1,000,000		1,000,000
Total		$ 27,000,000		$ 31,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		3.09%		2.65%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		5.30%		5.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		4.90%		5.00%
Ultimate health care trend assumption rate (as a percent)		4.50%		4.50%
Period until ultimate trend rate is reached (in years)		$ 4		$ 5
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0		0		0
Interest cost		2,000,000		2,000,000		3,000,000
Expected return on plan assets		0		0		0
Amortization of prior service cost (credit)		(3,000,000)		(3,000,000)		(3,000,000)
Amortization of net loss		2,000,000		1,000,000		2,000,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	0		0		0
Net periodic postretirement benefit cost		1,000,000		0		2,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Plan amendments		0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		0		0
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation		0		0		0
Net benefit cost recognized for financial reporting		$ 1,000,000		$ 0		$ 2,000,000
Discount rate (as a percent)		2.65%		3.47%		4.32%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		0.00%		0.00%		0.00%
Expected average long-term rate of return on assets (as a percent)		4.10%		4.50%		4.50%

[1] See Note 8 for further information on fair value measurement inputs and methods.

[2] A settlement charge is required when the amount of lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In 2021, as a result of lump-sum distributions during the 2021 plan year, NSP-Minnesota recorded a total pension settlement charge of $35 million in 2021, which was not recognized due to the effects of regulation. There were no settlement charges recorded to the qualified pension plans in 2020 and 2019.

[3] See Note 8 for further information on fair value measurement inputs and methods.