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]
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standards	$ 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	783				783
Other comprehensive income (loss), net of tax	(75)						(75)
Dividends declared on preferred stock	(34)				(34)
Dividends declared on common stock	(135)				(135)
Stock option exercises and other	49			(12)		61
Share-based compensation	47			47
Other	3			9		(6)
Ending balance (shares) at Mar. 31, 2018			1,488
Ending balance at Mar. 31, 2018	19,330	2,793	$ 15	4,397	15,222	(2,837)	(260)
Beginning balance at Dec. 31, 2018	20,670	2,793	$ 15	4,499	17,329	(3,714)	(252)
Beginning balance (shares) at Dec. 31, 2018			1,488
Increase (Decrease) in Stockholders' Equity
Net income	964				964
Other comprehensive income (loss), net of tax	181						181
Dividends declared on preferred stock	(34)				(34)
Dividends declared on common stock	(228)				(228)
Stock option exercises and other	26			(14)		40
Share-based compensation	53			53
Other	(7)			10	(14)	(3)
Ending balance (shares) at Mar. 31, 2019			1,488
Ending balance at Mar. 31, 2019	$ 21,625	$ 2,793	$ 15	$ 4,548	$ 18,017	$ (3,677)	$ (71)