Retirement Benefits - Assumptions (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.35%	4.40%		4.00%
Rate of compensation increase	4.50%	4.50%		4.50%
Medical trend rate1		7.60%		6.80%
Benefit Cost Assumptions
Discount rate	4.40%	4.40%	4.50%
Return on plan assets	7.00%	7.00%	6.75%
Rate of compensation increase	4.50%	4.50%	4.50%
Medical trend rate1		7.60%	9.50%
Nonqualified Plan \| Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.35%	4.40%		4.00%
Rate of compensation increase	4.50%	4.50%		4.50%
Medical trend rate1	0.00%	0.00%		0.00%
Benefit Cost Assumptions
Discount rate	4.40%	4.40%	4.50%
Return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	4.50%	4.50%	4.50%
Medical trend rate1	0.00%	0.00%	0.00%
Qualified Plan \| Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.35%	4.40%		4.00%
Rate of compensation increase	4.50%	4.50%		4.50%
Medical trend rate1	0.00%	0.00%		0.00%
Benefit Cost Assumptions
Discount rate	4.40%	4.40%	4.50%
Return on plan assets	7.50%	7.50%	7.45%
Rate of compensation increase	4.50%	4.50%	4.50%
Medical trend rate1	0.00%	0.00%	0.00%

Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Medical Cost Trend Rate

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- Definition

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

+ 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://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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