Earnings Per Share - Reconciliation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Basic	$ 1,124	$ 1,800	$ 2,099	$ 3,392
Diluted	$ 1,124	$ 1,800	$ 2,099	$ 3,392
Basic	1,269	1,300	1,273	1,303
Assumed exercise of stock options	7	11	5	9
Unvested restricted stock	4	4	4	4
Diluted	1,280	1,315	1,282	1,316
Basic	$ 0.89	$ 1.38	$ 1.65	$ 2.60
Diluted	$ 0.88	$ 1.37	$ 1.64	$ 2.58