Stock Compensation - Additional Information (Details) - USD ($) shares in Millions, $ in Millions		3 Months Ended
Mar. 31, 2017	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from exercise of stock options		$ 4
Options exercised in the period		0.3
Cash paid to settle RSUs		$ 1
Stock compensation expense		4	$ 2
Total unrecognized compensation cost related to nonvested awards granted and expected to vest	$ 36	$ 36
Weighted-average period in which the total unrecognized compensation cost is expected to be recognized	2 years 2 months 12 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in period		0.4

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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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

+ References

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- Definition

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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- Definition

Amount of cash paid related to share-based compensation liabilities.

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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 share instruments newly issued under a share-based compensation plan.

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Number of share options (or share units) exercised during the current period.

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