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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income—basic and diluted	$ 484	$ 248	$ 167	$ 1,371
Denominator:
Basic weighted-average common shares outstanding (in shares)	160.9	163.3	161.3	163.2
Diluted weighted-average shares	162.0	165.6	162.5	165.1
Earnings per share:
Basic (in USD per share)	$ 3.01	$ 1.51	$ 1.03	$ 8.40
Diluted (in USD per share)	$ 2.99	$ 1.49	$ 1.03	$ 8.30
Number of anti-dilutive stock-based awards (in shares)	1.4	0.0	1.4	0.4
Stock Options
Denominator:
Effect of stock-based awards (in shares)	0.5	1.4	0.7	1.2
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.9	0.5	0.7