Pensions and Other Benefits - Pension Plan Asset Allocation and Weighted-Average Policy Range (Details) - Pension Plan, Defined Benefit	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	100.00%
Percentage of plan assets	100.00%	100.00%
Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	1.20%
Percentage of plan assets	2.00%	0.90%
Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	24.10%
Percentage of plan assets	28.10%	24.60%
Public equities
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	45.10%
Percentage of plan assets	49.30%	54.50%
Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	9.80%
Percentage of plan assets	6.30%	6.80%
Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	9.80%
Percentage of plan assets	3.30%	2.40%
Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	10.00%
Percentage of plan assets	11.00%	10.80%
Minimum | Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	—
Minimum | Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	20
Minimum | Public equities
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	35
Minimum | Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	4
Minimum | Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	4
Minimum | Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	4
Maximum | Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	10
Maximum | Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	40
Maximum | Public equities
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	55
Maximum | Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	13
Maximum | Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	13
Maximum | Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Weighted-average policy range	13