Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic
Income from continuing operations	$ 2,430	$ 2,760	$ 5,107	$ 4,705
Income (loss) from discontinued operations, net of tax	(770)	106	(839)	114
Net income attributable to common stockholders	$ 1,660	$ 2,866	$ 4,268	$ 4,819
Weighted-average common shares outstanding - basic (in shares)	1,497	1,548	1,501	1,547
Basic earnings per common share – continuing operations (in dollars per share)	$ 1.62	$ 1.78	$ 3.40	$ 3.05
Basic earnings (loss) per common share – discontinued operations (in dollars per share)	(0.51)	0.07	(0.56)	0.07
Basic earnings per common share (in dollars per share)	$ 1.11	$ 1.85	$ 2.84	$ 3.12
Diluted
Income from continuing operations – diluted	$ 2,430	$ 2,759	$ 5,107	$ 4,703
Income (loss) from discontinued operations, net of tax – diluted	(770)	106	(839)	114
Net income attributable to common stockholders – diluted	$ 1,660	$ 2,865	$ 4,268	$ 4,817
Dilutive effect of warrants and awards under stock incentive plans	22	33	24	33
Weighted-average common shares outstanding - diluted (in shares)	1,519	1,581	1,525	1,580
Diluted earnings per common share – continuing operations (in dollars per share)	$ 1.60	$ 1.74	$ 3.35	$ 2.98
Diluted earnings (loss) per common share – discontinued operations (in dollars per share)	(0.51)	0.07	(0.55)	0.07
Diluted earnings per common share (in dollars per share)	$ 1.09	$ 1.81	$ 2.80	$ 3.05
Potentially dilutive securities (in shares)	6	26	6	26