Pensions and Other Benefits - Actuarial Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate, Next fiscal year	5.50%	6.00%	7.00%
Benefit cost, Expected rate of return on fund assets	7.25%
Health care cost trend rate change	0.50%
Ultimate health care cost trend rate	5.00%
Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation, Discount rate	3.25%	4.01%	3.80%
Benefit obligation, Projected future salary increases	2.75%	2.75%	2.75%
Health care cost trend rate, Next fiscal year	5.50%	6.00%	7.00%
Benefit cost, Discount rate	4.01%	3.80%	4.02%
Benefit cost, Expected rate of return on fund assets	7.50%	7.75%	7.75%
Benefit cost, Projected future salary increases	2.75%	2.75%	2.75%