Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 622	$ 1,259	$ 1,546	$ 946	$ 980	$ 1,315	$ 1,485	$ 746	$ 4,373	$ 4,526	$ 659
Basic weighted average shares outstanding (shares)									751	797	836
Dilutive effect of share-based awards (shares)									4	7	9
Diluted weighted average shares outstanding (shares)									755	804	845
Basic earnings per share (usd per share)	$ 0.85	$ 1.70	$ 2.04	$ 1.22	$ 1.26	$ 1.67	$ 1.85	$ 0.91	$ 5.82	$ 5.68	$ 0.79
Diluted earnings per share (usd per share)	$ 0.84	$ 1.69	$ 2.03	$ 1.21	$ 1.25	$ 1.65	$ 1.83	$ 0.90	$ 5.79	$ 5.63	$ 0.78