Earnings Per share - Schedule of Computation for Earnings Per Share Types (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 1,315	$ 357	$ 3,546	$ 1,371
Basic weighted average shares outstanding	788	834	803	840
Dilutive effect of share-based awards	7	9	8	9
Diluted weighted average shares outstanding	795	843	811	849
Basic earnings per share (in USD per share)	$ 1.67	$ 0.43	$ 4.42	$ 1.63
Diluted earnings per share (in USD per share)	$ 1.65	$ 0.42	$ 4.37	$ 1.61