Pension and Other Postretirement Benefits - Assumptions Used in Determining Benefit Obligations and Net Periodic Benefit Cost Amounts (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Weighted average assumptions for benefit obligations at year end:
Discount rate	2.20%	3.10%
Salary increase	3.50%	3.60%
Weighted average assumptions for net periodic cost for the year:
Discount rate	3.10%	2.80%
Salary increase	3.60%	3.60%
Expected return on assets	5.00%	5.50%
Other Benefits
Weighted average assumptions for benefit obligations at year end:
Discount rate	2.90%	3.70%
Weighted average assumptions for net periodic cost for the year:
Discount rate	3.70%	3.30%
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	5.60%	5.80%
Rate that the cost trend rate gradually declines to	5.00%	5.00%
Cash & equivalents | Pension Benefits
Weighted average assumptions for benefit obligations at year end:
Cash balance interest credit rate	4.00%	4.70%
Weighted average assumptions for net periodic cost for the year:
Cash balance interest credit rate	4.70%	4.70%