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Stock-Based Compensation - Intrinsic Value of Options Exercised and Cash Received (Details) - NQSOs - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 10	$ 1	$ 0
Cash received from options exercised	$ 24	$ 4	$ 0
Options exercised (in shares)	969,058		0

X

- Definition

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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