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Retirement Benefits and Trusteed Assets (Pension Plan - Assumptions used in Determining the PBO and Net Pension Costs) (Details) - Pension plan
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Projected benefit obligation      
Discount rate 2.91% 2.57% 3.28%
Rate of compensation increase 3.80% 3.80% 3.85%
Cash balance interest crediting rate 2.40% 2.00% 3.30%
Net pension costs      
Discount rate 2.57% 3.28% 4.40%
Rate of compensation increase 3.80% 3.85% 3.85%
Expected long-term rate of return on plan assets 7.00% 7.10% 7.30%
Cash balance interest crediting rate 2.00% 3.30% 3.70%