Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income—basic and diluted	$ 153	$ 484	$ 1,476	$ 167
Denominator:
Basic weighted-average common shares outstanding (in shares)	161.1	160.9	161.1	161.3
Diluted weighted-average shares	162.9	162.0	162.8	162.5
Earnings (loss) per share:
Basic (in USD per share)	$ 0.95	$ 3.01	$ 9.16	$ 1.03
Diluted (in USD per share)	$ 0.94	$ 2.99	$ 9.07	$ 1.03
Number of anti-dilutive stock-based awards (in shares)	0.4	1.4	0.9	1.4
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.2	0.5	1.1	0.7
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.6	0.6	0.5