Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total		Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock, at cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2016	$ 16,421		$ 2,783	$ 15	$ 4,267	$ 12,649	$ (3,130)	$ (163)
Beginning balance (shares) at Dec. 31, 2016				1,488
Increase (Decrease) in Stockholders' Equity
Net income	1,139	[1]				1,139
Other comprehensive income (loss), net of tax	51							51
Dividends declared on preferred stock	(78)					(78)
Dividends declared on common stock	(215)					(215)
Stock option exercises and other	72				(26)		98
Share-based compensation and related tax effects	79				79
Other	20				16		4
Ending balance (shares) at Jun. 30, 2017				1,488
Ending balance at Jun. 30, 2017	17,489		2,783	$ 15	4,336	13,495	(3,028)	(112)
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards (Note 2) | Accounting Standards Update 2014-09 and 2018-02 [Member]	167					200		(33)
Beginning balance at Dec. 31, 2017	18,525		2,793	$ 15	4,353	14,408	(2,892)	(152)
Beginning balance (shares) at Dec. 31, 2017				1,488
Increase (Decrease) in Stockholders' Equity
Net income	1,649					1,649
Other comprehensive income (loss), net of tax	(93)							(93)
Dividends declared on preferred stock	(83)					(83)
Dividends declared on common stock	(271)					(271)
Stock option exercises and other	99				(8)		107
Share-based compensation and related tax effects	78				78
Other	26				24		2
Ending balance (shares) at Jun. 30, 2018				1,488
Ending balance at Jun. 30, 2018	$ 20,097		$ 2,793	$ 15	$ 4,447	$ 15,903	$ (2,783)	$ (278)

[1] Adjusted for the retrospective adoption of ASU 2016-18. See Note 2.