Stock Benefit Plans - Weighted-average Assumptions (Details) - Long Term Incentive Plan - Stock Options	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CEO
Stock Benefit Plans
Risk-free interest rate	1.59%	2.52%	1.64%
Expected life (in years)	3 years 8 months 1 day	3 years 10 months 6 days	3 years 10 months 6 days
Expected volatility	28.62%	23.20%	21.89%
Expected dividend yield	6.47%	4.67%	4.22%
Employees
Stock Benefit Plans
Risk-free interest rate	1.42%	2.67%	1.56%
Expected life (in years)	3 years 8 months 1 day	3 years 8 months 4 days	3 years 10 months 6 days
Expected volatility	26.96%	22.51%	22.70%
Expected dividend yield	6.12%	4.54%	4.42%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

Rate of weighted-average expected volatility for award under share-based payment arrangement.

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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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No definition available.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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