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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic EPS:
Net income	$ 737	$ 1,693	$ 2,387	$ 4,329
Weighted-average common shares outstanding (in thousands)	525,415	661,869	564,886	682,337
Basic EPS (in dollars per share)	$ 1.40	$ 2.56	$ 4.23	$ 6.34
Diluted EPS:
Net income for purposes of computing diluted EPS	$ 737	$ 1,693	$ 2,387	$ 4,329
Share computation for diluted EPS (in thousands):
Basic weighted average common shares outstanding	525,415	661,869	564,886	682,337
Dilutive effect of stock awards	3,095	18,870	3,793	19,423
Diluted weighted average common shares outstanding	528,510	680,739	568,679	701,760
Diluted EPS (in dollars per share)	$ 1.40	$ 2.49	$ 4.20	$ 6.17
Stock options, stock appreciation rights and restricted stock unit awards excluded because inclusion would be antidilutive	1,623	1,094	1,771	667