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Income Taxes - NPC - Reconciliation of Effective Income Tax Rate (Details)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Income Tax Contingency [Line Items]      
Federal statutory income tax rate 21.00% 21.00% 21.00%
Effects of ratemaking (4.00%) (3.00%) (6.00%)
Other, net 0.00% (1.00%) (1.00%)
Effective income tax rate (21.00%) 4.00% (25.00%)
NPC      
Income Tax Contingency [Line Items]      
Federal statutory income tax rate 21.00% 21.00% 21.00%
Effects of ratemaking (11.00%) (8.00%) 0.00%
Other, net 1.00% 1.00% 1.00%
Effective income tax rate 11.00% 14.00% 22.00%