Retirement Benefits - Schedule of Assumptions Used to Determine Benefit Obligations (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Medical and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (percentage)	2.28%	3.19%
Ultimate healthcare trend rate (percentage)	4.50%	4.50%
Initial healthcare trend rate (pre 65/post 65) (percentage)	6.50%	5.50%
Qualified Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (percentage)	2.52%	3.28%	4.27%
Nonqualified Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (percentage)	2.51%	3.30%

Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Ultimate Health Care Cost Trend Rate

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- Definition

Defined Benefit Plan, Benefit Obligation, Health Care Cost Trend Rate Assumed, Next Fiscal Year

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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

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.

+ References

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