Regulatory Plant Decommissioning Recovery (Details) $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Regulatory Plant Decommissioning Recovery [Abstract]
Percentage Of Total Obligation For Decommissioning Expected To Be Funded By External Funds		100.00%
Assumed annual escalation rate during plant removal activities		4.36%	4.36%
Assumed annual escalation rate during spent fuel management and site restoration activities		3.36%	3.36%
Approved annual accrual for decommissioning costs		$ 14	$ 14	$ 14
Funded Status of Nuclear Decommissioning Obligation [Abstract]
Estimated decommissioning cost obligation from most recently approved study (in 2014 dollars)		3,012	3,012
Effect of escalating costs		688	539
Estimated decommissioning cost obligation (in current dollars)		3,700	3,551
Effect of escalating costs to payment date		7,505	7,654
Estimated future decommissioning costs (undiscounted)		11,205	11,205
Effect of discounting obligation (using average risk-free interest rate of 2.39% and 3.33% for 2019 and 2018, respectively)		(5,562)	(6,911)
Discounted decommissioning cost obligation		5,643	4,294
Underfunding of external decommissioning fund compared to the discounted decommissioning obligation		(3,203)	(2,239)
Regulatory Basis to GAAP Basis Reconciliation [Abstract]
Differences in Discount Rate and Market Risk Premium		(2,295)	(1,447)
Operating and Maintenance Costs Not Included for GAAP		(1,280)	(879)
Asset Retirement Obligation		2,701	2,568	2,475
Annual Decommissioning Recorded As Depreciation Expense [Abstract]
Annual decommissioning recorded as depreciation expense: (a) (b)	[1],[2]	$ 20	20	20
Minimum
Regulatory Plant Decommissioning Recovery [Abstract]
Assumed after tax rate of return used to determine funding for external decommissioning trust fund		5.23%
Maximum
Regulatory Plant Decommissioning Recovery [Abstract]
Assumed after tax rate of return used to determine funding for external decommissioning trust fund		6.30%
Nuclear Plant [Member]
Regulatory Basis to GAAP Basis Reconciliation [Abstract]
Asset Retirement Obligation		$ 2,068	1,968	$ 1,874
Fair Value Measured on a Recurring Basis | Nuclear Decommissioning Fund
Funded Status of Nuclear Decommissioning Obligation [Abstract]
Decommissioning Fund Investments		2,440	2,055
Annual Decommissioning Recorded As Depreciation Expense [Abstract]
Decommissioning Fund Investments, Fair Value		$ 2,440	$ 2,100
Measurement Input, Risk Free Interest Rate
Public Utilities, General Disclosures [Line Items]
Debt Instrument, Measurement Input		0.0239	0.0333

[1] Decommissioning expense does not include depreciation of the capitalized nuclear asset retirement costs.

[2] Decommissioning expenses in 2019, 2018 and 2017 include Minnesota’s retail jurisdiction annual funding requirement of approximately $14 million.