Benefit Plans - Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension benefits
Weighted average assumptions used in net periodic benefit cost:
Discount rate	2.61%	2.70%	2.91%
Rate of compensation increase	2.33%	2.41%	4.00%
Expected long-term rate of return on assets	5.10%	5.54%	6.71%
Weighted average assumptions used in benefit obligations:
Discount rate	2.10%	2.79%
Rate of compensation increase	2.58%	2.49%
Other retirement benefits
Weighted average assumptions used in net periodic benefit cost:
Discount rate	3.20%	4.20%	3.45%
Weighted average assumptions used in benefit obligations:
Discount rate	2.30%	4.20%