Credit Facility (Details) - Credit Facility $ in Millions		12 Months Ended
		Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Line of Credit Facility [Line Items]
Line Of Credit Facility Debt To Total Capitalization Ratio	[1]	46.10%	45.70%
Line Of Credit Facility Maximum Amount Credit Facility May Be Increased		$ 50
Number Of Additional Periods Revolving Termination Date Can Be Extended Subject To Majority Bank Group Approval	[2]	2
Line Of Credit Facility Maximum Debt To Total Capitalization Ratio Allowed		65.00%
Line Of Credit Facility Minimum Threshhold Percentage Of Subsidiary Assets To Consolidated Assets Required To Initiate Cross Default Provisions		15.00%
Line of Credit Facility, Minimum Amount of Indebtedness in Default to Initiate Cross Default Provisions		$ 75
Direct advances on the credit outstanding		0	$ 0
SPS [Member]
Line of Credit Facility [Line Items]
Credit facility	[3]	500
Drawn	[4]	75
Available		$ 425

[1] The credit facility has a financial covenant requiring that the debt-to-total capitalization ratio be less than or equal to 65%.

[2] All extension requests are subject to majority bank group approval.

[3] This credit facility matures in September 2027.

[4] Includes letters of credit and outstanding commercial paper.