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, 2020	Mar. 31, 2019
Numerator:
Net income (loss)—basic and diluted	$ (1,226)	$ 695
Denominator:
Basic weighted-average common shares outstanding (in shares)	162.2	163.0
Diluted weighted-average shares	162.2	164.6
Earnings per share:
Basic (in USD per share)	$ (7.56)	$ 4.27
Diluted (in USD per share)	$ (7.56)	$ 4.22
Number of anti-dilutive stock-based awards (in shares)	2.5	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	0.0	0.9
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.0	0.7