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Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Statement of Comprehensive Income [Abstract]      
Tax benefit on net other comprehensive loss recognized during the period for postretirement benefit plans $ 292 $ 586 $ 136
Tax expense on amounts reclassified from accumulated other comprehensive loss during the period for postretirement benefit plans $ 119 $ 247 $ 327