v3.20.4

Pension And Postretirement Benefits (Other Changes Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Roll Forward] |  |  |
Prior service (cost) credit | $ 2,250 | $ 3,457 | $ 830
Amortization of prior service credit | (1,841) | (1,459) | (1,322)
Pension Benefits |  |  |
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Roll Forward] |  |  |
Balance at beginning of year | 361 | 447 | 571
Prior service (cost) credit | 250 | 0 | (37)
Amortization of prior service credit | (86) | (86) | (87)
Total recognized in other comprehensive (income) loss | 164 | (86) | (124)
Balance at end of year | 525 | 361 | 447
Postretirement Benefits |  |  |
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Roll Forward] |  |  |
Balance at beginning of year | 8,171 | 6,086 | 6,456
Prior service (cost) credit | 2,001 | 3,457 | 864
Amortization of prior service credit | (1,756) | (1,372) | (1,234)
Total recognized in other comprehensive (income) loss | 245 | 2,085 | (370)
Balance at end of year | $ 8,416 | $ 8,171 | $ 6,086

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