Stock-Based Compensation (Discount Stock Plan) (Details) shares in Millions	12 Months Ended
Dec. 31, 2019 $ / shares shares
Discount Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount to the market price, percentage	85.00%
Measurement performance period, years	1 year
Average 2019 purchase price per share (net of discount) (in dollars per share) \| $ / shares	$ 35.62
2019 number of shares purchased by employees (in shares)	0.2
Shares purchased since inception in 1982 (in shares)	23.3
Maximum shares under the plan (in shares)	27.0
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	66.00%
Performance measurement period	3 years
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	33.00%
Vesting period	3 years

Average price per share employee purchase net of discount.

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Measurement Performance Period

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Number of shares purchased by employees

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Share-based Compensation Arrangement by Share-based Payment Award, Award Performance Period

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Shares purchased since inception in 1982

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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-Publisher FASB
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-Topic 718
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Discount rate from fair value on purchase date that participants pay for shares.

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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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Number of shares authorized for issuance under share-based payment arrangement.

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Percentage of vesting of award under share-based payment arrangement.

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