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Stock Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted (shares)			4.2
Stock option granted, weighted average exercise price per share			$ 10.12
Stock option granted, weighted average fair value per share			$ 1.97
Stock-based compensation expense	$ 9	$ 7	$ 23	$ 18
Unearned compensation cost related to the unvested portion of all stock-based awards	$ 26		$ 26
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)			0.6
Weighted average fair value per share granted (dollars per share)			$ 9.30
Performance Share Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)			0.2
Weighted average fair value per share granted (dollars per share)			$ 7.59