Equity (Stock-Based Compensation) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation
Stock based compensation costs	$ 82	$ 76	$ 77
Tax benefits related to stock-based compensation arrangements	21	$ 29	$ 30
Unrecognized stock based compensation costs	$ 98
Unrecognized stock based compensation costs weighted-average period of recognition (in years)	1 year 9 months
Common stock authorized for awards (in shares)	15,000,000
Number of additional shares available for grant (in shares)	0

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 total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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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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