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Trust Investments (Fair Values And Gross Unrealized Gains And Losses For The Securities Held) (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2022
Dec. 31, 2021
Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Trust Investments, Cost $ 2,154 $ 2,157
Gross Unrealized Gains 429 510
Gross Unrealized Losses (94) (32)
Trust Investments, Fair Value 2,489 [1] 2,635 [2]
NDT Fund Foreign Currency 2 2
Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Trust Investments, Cost 222 226
Gross Unrealized Gains 11 18
Gross Unrealized Losses (14) (2)
Trust Investments, Fair Value 219 242
Total Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 1,325 1,320
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 5 28
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (73) (14)
Debt Securities, Available-for-Sale, Fair Value 1,257 1,334
Total Debt Securities [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 207 212
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 1 6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (14) (2)
Debt Securities, Available-for-Sale, Fair Value 194 216
Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Equity Securities, Cost 829 837
Equity Securities, Accumulated Gross Unrealized Gain 424 482
Equity Securities, FV-NI, Unrealized Loss (21) (18)
Equity Securities, Fair Value 1,232 1,301
Unrealized Gains (Losses) on Equity Securities still held (47)  
Equity Securities [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Unrealized Gains (Losses) on Equity Securities still held (1)  
Corporate Debt Obligations [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 649 637
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 3 16
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (35) (6)
Debt Securities, Available-for-Sale, Fair Value 617 647
Corporate Debt Obligations [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 96 105
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 1 5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (6) (1)
Debt Securities, Available-for-Sale, Fair Value 91 109
Government Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 676 683
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 2 12
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (38) (8)
Debt Securities, Available-for-Sale, Fair Value 640 687
Government Debt Securities [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Debt Securities, Available-for-sale, Amortized Cost 111 107
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax (8) (1)
Debt Securities, Available-for-Sale, Fair Value 103 107
International Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Equity Securities, Cost 333 346
Equity Securities, Accumulated Gross Unrealized Gain 98 119
Equity Securities, FV-NI, Unrealized Loss (18) (15)
Equity Securities, Fair Value 413 450
Domestic Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
Equity Securities, Cost 496 491
Equity Securities, Accumulated Gross Unrealized Gain 326 363
Equity Securities, FV-NI, Unrealized Loss (3) (3)
Equity Securities, Fair Value 819 851
Domestic Equity Securities [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
Equity Securities, Cost 15 14
Equity Securities, Accumulated Gross Unrealized Gain 10 12
Equity Securities, FV-NI, Unrealized Loss 0 0
Equity Securities, Fair Value 25 $ 26
Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]    
Schedule of Trust Investments [Line Items]    
After tax amount of net unrealized gains recognized in AOCI (40)  
Debt Securities [Member] | Rabbi Trust [Member]    
Schedule of Trust Investments [Line Items]    
After tax amount of net unrealized gains recognized in AOCI $ (10)  
[1] The NDT Fund Investments table excludes foreign currency of $2 million as of March 31, 2022, which is part of the NDT Fund.
[2] The NDT Fund Investments table excludes foreign currency of $2 million as of December 31, 2021, which is part of the NDT Fund.