Share-based Compensation - Share-based Compensation Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense before income taxes	$ 79	$ 85	$ 72
Income tax benefit on share-based compensation expense	0	0	0
Restricted Stock
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense before income taxes	51	53	40
Performance Share Units
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense before income taxes	18	22	22
Stock Options
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense before income taxes	$ 10	$ 10	$ 10