Earnings (Loss) Per Common Share - Computation of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings
Net income	$ 249	$ 273
Less: Preferred stock dividends	5	5
Net income available to common stockholders	$ 244	$ 268
Shares
Weighted average common shares outstanding, basic	358.2	358.5
Dilutive effect of stock-based awards under compensation plans	4.0	2.6
Weighted average common shares outstanding and dilutive potential common shares	362.2	361.1
Earnings Per Share, Basic [Abstract]
Net income available to common stockholders	$ 0.68	$ 0.75
Earnings Per Share, Diluted [Abstract]
Net income available to common stockholders	$ 0.67	$ 0.74