Earnings (Loss) per Share - Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic EPS:
Net income	$ 234	$ 700
Weighted average common shares outstanding (in thousands)	503,902	606,245
Basic EPS (in dollars per share)	$ 0.46	$ 1.15
Diluted EPS:
Net income for purposes of computing diluted EPS	$ 234	$ 700
Share computation for diluted EPS (in thousands):
Basic weighted average common shares outstanding	503,902	606,245
Dilutive effect of stock awards	3,895	5,243
Diluted weighted average common shares outstanding	507,797	611,488
Diluted EPS (in dollars per share)	$ 0.46	$ 1.14
Restricted stock unit awards excluded from the calculation of diluted EPS because inclusion would be antidilutive	395	1,089