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Pension and Other Postretirement Benefits - Weighted average assumptions used to determine net periodic benefit cost (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Rate of compensation increase, year one	3.00%
Rate of compensation increase, year one and thereafter	3.50%
Rate of compensation increase, year two		3.00%	3.00%
Rate of compensation increase, year two and thereafter		4.00%	4.00%
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Measurement date	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fiscal year end	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Discount rate	4.38%	3.69%	4.15%
Rate of compensation increase, group 1	3.00%	3.00%	3.00%
Rate of compensation increase, group 2	3.50%	4.00%	4.00%
Expected return on plan assets	7.25%	7.18%	6.82%
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Measurement date	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fiscal year end	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Discount rate	4.29%	3.66%	4.05%
Rate of compensation increase, group 1	3.00%	3.00%	3.00%
Rate of compensation increase, group 2	3.50%	4.00%	4.00%
Expected return on plan assets	0.00%	0.00%	0.00%

X

- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase, Year One

+ References

No definition available.

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- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase, Year One And Thereafter

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- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase, Year Two

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- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase, Year Two And Thereafter

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Year end for fiscal year

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- Definition

The date(s) used to measure (at least the majority of) plan assets and benefit obligations for defined benefit pension and other postretirement benefit plans.

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- Definition

The maximum expected rate of compensation increases (for pay-related plans).

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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

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 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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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