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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income (loss)—basic and diluted	$ 909	$ 428	$ (317)	$ 1,123
Denominator:
Basic weighted-average common shares outstanding (in shares)	160.8	163.3	161.5	163.1
Diluted weighted-average shares	161.5	165.2	161.5	164.9
Earnings per share:
Basic (in USD per share)	$ 5.65	$ 2.62	$ (1.96)	$ 6.89
Diluted (in USD per share)	$ 5.63	$ 2.59	$ (1.96)	$ 6.81
Number of anti-dilutive stock-based awards (in shares)	2.7	0.4	2.6	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	0.3	1.2	0.0	1.1
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.4	0.7	0.0	0.7