Retirement Plans - Assumptions for Determining Projected Benefit Obligation and Net Periodic Cost of Defined Benefit Pension Plans (Details) - Defined Benefit Pension Plans - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
For determining net periodic cost for the year:
Increase in plan liability, if discount rate were reduced by 25 basis points	$ 57,000,000
Minimum
For determining projected benefit obligation ("PBO") at year-end:
Discount rate	80.00%	120.00%	180.00%
Rate of increase in compensation levels	225.00%	225.00%	225.00%
For determining net periodic cost for the year:
Discount rate	120.00%	180.00%	190.00%
Rate of increase in compensation levels	225.00%	225.00%	225.00%
Expected long-term rate of return on assets	120.00%	180.00%	190.00%
Maximum
For determining projected benefit obligation ("PBO") at year-end:
Discount rate	3.50%	4.75%	7.25%
Rate of increase in compensation levels	6.00%	6.00%	7.00%
For determining net periodic cost for the year:
Discount rate	4.75%	7.25%	5.50%
Rate of increase in compensation levels	6.00%	7.00%	7.00%
Expected long-term rate of return on assets	5.60%	8.20%	7.00%
Expected contributions in next fiscal year	$ 12,000,000

The effect on the defined benefit plan obligation of a 25 basis-point decrease in the interest rate.

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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.

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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.

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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.

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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://www.xbrl.org/2003/role/disclosureRef
-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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920

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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.

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- Definition

Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921

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