Nuclear Obligations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Canister	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Decommissioning Fund Investments, Fair Value	$ 2,055
Fuel Disposal [Abstract]
DOE fuel disposal assessments included in fuel expense		$ 0
Regulatory Plant Decommissioning Recovery [Abstract]
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%
Percentage Of Total Obligation For Decommissioning Expected To Be Funded By External Funds	100.00%
Approved annual accrual for decommissioning costs	$ 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	539	396
Estimated decommissioning cost obligation (in current dollars)	3,551	3,408
Effect of escalating costs to payment date	7,654	7,797
Estimated future decommissioning costs (undiscounted)	11,205	11,205
Effect of discounting obligation (using average risk-free interest rate of 3.33% and 2.80% for 2018 and 2017, respectively)	(6,911)	(6,398)
Discounted decommissioning cost obligation	4,294	4,807
Underfunding of external decommissioning fund compared to the discounted decommissioning obligation	(2,239)	(2,664)
Regulatory Basis to GAAP Basis Reconciliation [Abstract]
Differences in Discount Rate and Market Risk Premium	(1,447)	(1,403)
Operating and Maintenance Costs Not Included for GAAP	(879)	(1,041)
ARO differences between 2017 and 2014 cost studies	0	(489)
Asset Retirement Obligation	2,568	2,475	$ 2,782
Annual Decommissioning Recorded As Depreciation Expense [Abstract]
Annual decommissioning recorded as depreciation expense: (a) (b)	$ 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	$ 1,968	1,874	$ 2,249
Monticello [Member]
Fuel Disposal [Abstract]
Number of authorized canisters filled and placed In dry cask nuclear storage facility | Canister	30
Prairie Island [Member]
Fuel Disposal [Abstract]
Number of authorized canisters filled and placed In dry cask nuclear storage facility | Canister	44
Number of authorized canisters in dry cask nuclear storage facility | Canister	64
Fair Value | Fair Value Measured on a Recurring Basis | Nuclear Decommissioning Fund
Funded Status of Nuclear Decommissioning Obligation [Abstract]
Assets Held in External Decommissioning Trust		$ 2,143
Measurement Input, Risk Free Interest Rate
Public Utilities, General Disclosures [Line Items]
Measurement input (as a percent)	0.0333	0.0280