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Health care rate assumptions and cost trend rate (Details 6) - Overfunded Plan - Qualified Plan - Other Postretirement Benefits
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]    
Health care trend rate assumed for next year 7.00% 7.00%
Health care cost trend rate - ultimate 4.50% 4.50%
Year in which ultimate trend rate achieved 2031 2031