Capital Stock - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock cash dividends paid	$ 37	$ 148	$ 138
Dividends, share-based compensation	1	2	1
Common stock repurchased	0	0	220
Common Stock
Class Of Stock [Line Items]
Common stock cash dividends paid	$ 37	$ 148	138
Common stock repurchased			$ 220
Common stock repurchased (in shares)	0	0	8,936,302
Common Stock | Payments for Share Repurchases Related to Employee Stock Based Compensation
Class Of Stock [Line Items]
Common stock repurchased (in shares)	0	0	0