Employee Benefit Plans - Assumptions used (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension \| Retirement Income Plan
Weighted-average assumptions used to determine obligations (balance sheet):
Discount rate	3.00%	3.95%	3.35%
Rate of compensation increase		3.50%	3.50%
Weighted-average assumptions used to determine net periodic benefit cost (statement of operations):
Discount rate	3.95%	3.35%	3.75%
Expected return on plan assets	6.50%	7.00%	7.00%
Rate of compensation increase	3.50%	3.50%	3.50%
Pension \| National Service-Related Pension Plan
Weighted-average assumptions used to determine obligations (balance sheet):
Discount rate	3.25%	4.15%	3.65%
Weighted-average assumptions used to determine net periodic benefit cost (statement of operations):
Discount rate	4.15%	3.65%	4.15%
Expected return on plan assets	6.50%	7.00%	7.00%
Pension \| Superannuation
Weighted-average assumptions used to determine obligations (balance sheet):
Discount rate	2.30%	3.70%	3.70%
Rate of compensation increase	3.25%	3.25%	4.00%
Weighted-average assumptions used to determine net periodic benefit cost (statement of operations):
Discount rate	3.70%	3.70%	4.20%
Expected return on plan assets	5.00%	6.00%	6.00%
Rate of compensation increase	3.25%	4.00%	4.00%
Other Post-Retirement Benefits
Weighted-average assumptions used to determine obligations (balance sheet):
Discount rate	2.55%	3.70%	3.10%
Weighted-average assumptions used to determine net periodic benefit cost (statement of operations):
Discount rate	3.70%	3.10%	3.40%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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