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Income Taxes - NPC - Reconciliation of Effective Income Tax Rate (Details)
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Income Tax Contingency [Line Items]      
Federal statutory income tax rate 21.00% 21.00% 21.00%
Effects of ratemaking (11.00%) (16.00%) (4.00%)
Other, net 0.00% 2.00% 1.00%
Effective income tax rate (87.00%) (136.00%) (21.00%)
NPC      
Income Tax Contingency [Line Items]      
Federal statutory income tax rate 21.00% 21.00% 21.00%
Effects of ratemaking (13.00%) (11.00%) (11.00%)
Other, net 0.00% 1.00% 1.00%
Effective income tax rate 8.00% 11.00% 11.00%