Stock-Based Compensation (Narrative) (Details) shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) shares
Stock-Based Compensation [Abstract]
Equity-classified awards, unrecognized compensation cost	$ 49
Equity-classified awards, weighted average period over which unrecognized cost is recognized, years	2 years
Liability-classified restricted stock, vesting period	4 years
Liability-classified restricted stock, unvested \| shares	12
Liability-classified restricted stock, unrecognized compensation cost	$ 51
Liability-classified restricted stock, weighted average period over which unrecognized cost is recognized, years	4 years
Liability-classified performance units, vesting period	3 years
Liability-classified performance units, unvested \| shares	3
Liability-classified performance units, unrecognized compensation cost	$ 14
Liability-classified performance units, weighted average period over which unrecognized cost is recognized, years	3 years

Unrecognized cost of unvested liability-based performance units share-based compensation awards.

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Unrecognized cost of unvested liability-based restricted stock share-based compensation awards.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

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- Definition

Period which an employee's right to exercise liability-based performance units are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The number of non-vested liability-based performance units, that validly exist and are outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

The number of non-vested liability-based restricted stock, that validly exist and are outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Period which an employee's right to exercise liability-based restricted stock award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

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- References

No definition available.

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