Stock Plans (Narrative) (Details) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($) ShareBasedCompensationPlan $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plan under which grants were made \| ShareBasedCompensationPlan	7
Number of stock-based compensation plan under which grants were not made \| ShareBasedCompensationPlan	6
EIP Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under the plans (in shares) \| shares	5,667,000
Shares available for grant under the plan (in shares) \| shares	2,636,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period	$ 3	$ 0
Shares granted (in shares) \| shares	284,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period	$ 10	$ 14
Shares granted (in shares) \| shares	2,023,000	454,000
Restricted Stock
Restricted stock granted, Aggregate fair value	$ 13	$ 5
Restricted stock vested, fair value	1	3
Fair value of unvested restricted stock	$ 12	$ 8	$ 4
Restriced stock, grant date fair value per share \| $ / shares	$ 16.08	$ 47.77	$ 58.63
Remaining unrecognized compensation cost associated with unvested restricted stock awards	$ 28
Weighted average period over which unvested restricted stock awards unrecognized compensation cost is expected to be recognized (in years)	2 years

Number of stock-based compensation plan under which grants were made and remained outstanding.

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Number Of Stock Based Compensation Plan Under Which Grants Were Not Made

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Restricted Stock

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The total fair value of equity-based awards, other than options, for which the grantee received an unvested equity-based award during the reporting period, subject to satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The total fair value of equity-based awards other than options outstanding as of the balance sheet date.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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