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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings
Income (loss) from continuing operations, net of tax	$ 434	$ (152)	$ 862	$ 151
Income from discontinued operations, net of tax	148	112	317	187
Net income (loss)	$ 582	$ (40)	$ 1,179	$ 338
Shares
Weighted average common shares outstanding, basic	358.3	366.0	357.9	368.7
Dilutive effect of stock compensation plans	4.0	0.0	4.2	4.0
Dilutive effect of warrants	1.9	0.0	2.0	2.8
Weighted average common shares outstanding and dilutive potential common shares	364.2	366.0	364.1	375.5
Earnings Per Share, Basic [Abstract]
Income (loss) from continuing operations, net of tax	$ 1.21	$ (0.42)	$ 2.41	$ 0.41
Income from discontinued operations, net of tax	0.41	0.31	0.88	0.51
Net income (loss) per common share	1.62	(0.11)	3.29	0.92
Earnings Per Share, Diluted [Abstract]
Income (loss) from continuing operations, net of tax	1.19	(0.42)	2.37	0.40
Income from discontinued operations, net of tax	0.41	0.31	0.87	0.50
Net income (loss) per common share	$ 1.60	$ (0.11)	$ 3.24	$ 0.90
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted Average Number of Shares Outstanding, Including Antidilutive Shares		372.3		372.3
Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		3.8
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		2.5