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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings
Income from continuing operations, net of tax	$ 427	$ 145	$ 1,289	$ 296
Income from discontinued operations, net of tax	5	89	322	276
Net income	$ 432	$ 234	$ 1,611	$ 572
Shares
Weighted average common shares outstanding, basic	358.6	360.2	358.1	365.9
Dilutive effect of stock compensation plans	3.6	4.5	4.0	4.1
Dilutive effect of warrants	1.9	2.3	2.0	2.6
Weighted average common shares outstanding and dilutive potential common shares	364.1	367.0	364.1	372.6
Earnings Per Share, Basic [Abstract]
Income from continuing operations, net of tax	$ 1.19	$ 0.40	$ 3.60	$ 0.81
Income from discontinued operations, net of tax	0.01	0.25	0.90	0.75
Net income per common share	1.20	0.65	4.50	1.56
Earnings Per Share, Diluted [Abstract]
Income from continuing operations, net of tax	1.17	0.40	3.54	0.79
Income from discontinued operations, net of tax	0.02	0.24	0.88	0.75
Net income per common share	$ 1.19	$ 0.64	$ 4.42	$ 1.54