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Employee Benefits - Assumptions (Details)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Plan | Benefit obligation assumptions        
Weighted average assumptions - benefit obligations        
Discount rate   2.67% 3.41% 4.30%
Rate of compensation increase   4.00% 4.00%  
Interest credit rate   3.69% 3.70%  
Pension Plan | Net periodic benefit cost assumptions        
Weighted average assumptions - net periodic benefit cost        
Discount rate   3.34% 4.21% 3.71%
Expected return on plan assets   6.87% 7.12% 7.12%
Rate of compensation increase   4.00% 3.66% 3.66%
Interest credit rate   3.70% 3.72% 3.71%
Pension Plan | Net periodic benefit cost assumptions | Subsequent event        
Weighted average assumptions - net periodic benefit cost        
Expected return on plan assets 6.87%      
OPEB Plan | Benefit obligation assumptions        
Weighted average assumptions - benefit obligations        
Discount rate   2.60% 3.39% 4.27%
OPEB Plan | Benefit obligation assumptions | Pre 65        
Medical cost trend rates        
Assumed medical cost trend rate   5.85% 6.00%  
Ultimate trend rate   5.00% 5.00%  
Year ultimate trend rate is reached   2028 2028  
OPEB Plan | Benefit obligation assumptions | Post 65        
Medical cost trend rates        
Assumed medical cost trend rate   5.80% 5.91%  
Ultimate trend rate   5.00% 5.00%  
Year ultimate trend rate is reached   2028 2028  
OPEB Plan | Net periodic benefit cost assumptions        
Weighted average assumptions - net periodic benefit cost        
Discount rate   3.39% 4.27% 3.63%
Expected return on plan assets   7.00% 7.25% 7.25%
OPEB Plan | Net periodic benefit cost assumptions | Subsequent event        
Weighted average assumptions - net periodic benefit cost        
Expected return on plan assets 7.00%      
OPEB Plan | Net periodic benefit cost assumptions | Pre 65        
Medical cost trend rates        
Assumed medical cost trend rate   6.00% 6.25% 6.50%
Ultimate trend rate   5.00% 5.00% 5.00%
Year ultimate trend rate is reached   2028 2024 2024
OPEB Plan | Net periodic benefit cost assumptions | Post 65        
Medical cost trend rates        
Assumed medical cost trend rate   5.91% 6.01% 6.09%
Ultimate trend rate   5.00% 5.00% 5.00%
Year ultimate trend rate is reached   2028 2028 2028