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
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net income (loss)—basic and diluted	$ 620	$ (1,226)
Denominator:
Basic weighted-average common shares outstanding (in shares)	161.0	162.2
Diluted weighted-average shares	162.5	162.2
Earnings per share:
Basic (in USD per share)	$ 3.85	$ (7.56)
Diluted (in USD per share)	$ 3.82	$ (7.56)
Number of anti-dilutive stock-based awards (in shares)	1.0	2.5
Stock Options
Denominator:
Effect of stock-based awards (in shares)	0.9	0.0
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.0