Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost 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=108410482&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=108410482&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=108410482&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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- Definition

The percentage who elected lump sum distributions.

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PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Rates Used to Estimate Our Net Periodic Benefit Costs (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018 Rate	Dec. 31, 2017 Rate	Dec. 31, 2016 Rate
Non Registered Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.00%	3.50%	3.50%	3.50%
Qualified and Registered Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.00%	8.00%
Canada
Defined Benefit Plan Disclosure [Line Items]
Discount rates, net periodic benefit cost		3.50%	3.70%
Pension \| Qualified and Registered Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		8.00%	8.00%	9.00%
Pension \| Plum Creek \| Qualified and Registered Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets			7.00%
Pension \| U.S.
Defined Benefit Plan Disclosure [Line Items]
Discount rates, net periodic benefit cost		3.70%	4.30%	4.50%
Pension \| U.S. \| Qualified and Registered Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Lump sum distributions election(2)		60.00%	60.00%	60.00%
Pension \| Canada
Defined Benefit Plan Disclosure [Line Items]
Discount rates, net periodic benefit cost				4.00%
Pension \| Salaried \| Canada
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		3.25%	3.50%	3.50%
Pension \| Hourly \| Canada
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		3.00%	3.25%	3.25%
Minimum \| Pension \| Salaried \| U.S.
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		2.00%	2.00%	2.00%
Minimum \| Pension \| Hourly \| U.S.
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		2.30%	2.30%	2.30%
Maximum \| Pension \| Salaried \| U.S.
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		13.00%	13.00%	13.00%
Maximum \| Pension \| Hourly \| U.S.
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase		13.00%	13.00%	13.00%