Equity - Share-based payments (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based compensation expense
Pre-tax compensation expense	$ 21	$ 26	$ 28
Income tax benefit	(3)	(8)	(11)
Total share-based compensation expense, net of income taxes	$ 18	18	17
Stock Incentive Plan
Shares authorized under Stock Incentive Plan	8.0
Shares available for future grants under Stock Incentive Plan	3.3
Employee Stock Option
Share-based compensation expense
Pre-tax compensation expense	$ 5	7	9
Income tax benefit	(1)	(2)	(3)
Total share-based compensation expense, net of income taxes	4	5	6
Restricted Stock Units (RSUs)
Share-based compensation expense
Pre-tax compensation expense	12	13	12
Income tax benefit	(2)	(4)	(5)
Total share-based compensation expense, net of income taxes	10	9	7
Performance shares and other share-based awards
Share-based compensation expense
Pre-tax compensation expense	4	6	7
Income tax benefit		(2)	(3)
Total share-based compensation expense, net of income taxes	$ 4	$ 4	$ 4

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
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The amount of expense, net of income tax, 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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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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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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