Note 6 - Earnings Per Common Share - Computation of Basic and Diluted Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Convertible Preferred Stock, Series A [Member]
Series A convertible preferred stock dividend	[1]	$ 24	$ 24	$ 49	$ 49
Effect of dilutive securities:
Effect of dilutive securities (in shares)		115	115	115	115
Stock Options and Other Dilutive Securities [Member]
Effect of dilutive securities:
Effect of dilutive securities (in shares)		8	10	8	11
Stock Compensation Plan [Member]
Antidilutive potential shares excluded from diluted earnings per common share:
Antidilutive potential shares excluded from diluted earnings per common share (in shares)		20	20	21	17
Net income		$ 2,207	$ 496	$ 1,839	$ 903
Net income available to common stockholders - basic		2,183	472	1,790	854
Net income available to common stockholders - diluted		$ 2,207	$ 496	$ 1,839	$ 903
Weighted-average common shares outstanding - basic (in shares)		1,059	1,246	1,081	1,257
Weighted-average common shares outstanding - diluted (in shares)		1,182	1,371	1,204	1,383
Basic earnings per common share (in dollars per share)		$ 2.06	$ 0.38	$ 1.66	$ 0.68
Diluted earnings per common share (in dollars per share)		$ 1.87	$ 0.36	$ 1.53	$ 0.65
Antidilutive potential shares excluded from diluted earnings per common share (in shares)		20	20	21	17

[1] In the three months ended September 30, 2015, the Series A convertible preferred stock was anti-dilutive and therefore excluded from the calculation of diluted earnings per share.