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, 2019	Mar. 31, 2018
Earnings
Income from continuing operations, net of tax	$ 630	$ 428
Less: Preferred stock dividends	5	0
Income from discontinued operations, net of tax, available to common stockholders	625	428
Income from discontinued operations, net of tax, available to common stockholders	0	169
Net Income (Loss) Available to Common Stockholders, Basic	$ 625	$ 597
Shares
Weighted average common shares outstanding, basic	360.0	357.5
Dilutive effect of stock-based awards under compensation plans	3.3	4.4
Dilutive effect of warrants	1.4	2.0
Weighted average common shares outstanding and dilutive potential common shares	364.7	363.9
Earnings Per Share, Basic [Abstract]
Income from continuing operations, net of tax, available to common stockholders	$ 1.74	$ 1.20
Income from discontinued operations, net of tax, available to common stockholders	0	0.47
Net income available to common stockholders	1.74	1.67
Earnings Per Share, Diluted [Abstract]
Income from continuing operations, net of tax, available to common stockholders	1.71	1.18
Income from discontinued operations, net of tax, available to common stockholders	0	0.46
Net income available to common stockholders	$ 1.71	$ 1.64