Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Series D Preferred Stock [Member]	Series E Preferred Stock [Member]	Series F Preferred Stock [Member]	Series G Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series D Preferred Stock [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Retained Earnings [Member] Series F Preferred Stock [Member]	Retained Earnings [Member] Series G Preferred Stock [Member]	Treasury Stock, at Cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,450	$ 1,257	$ 6,331	$ 11,556					$ (4,181)	$ (818)	$ 1
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2018						946,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2018							1,019,503,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,450	$ 1,257	6,259	11,771					(4,283)	(530)	2
Net income (loss)	$ 407								407							0
Other comprehensive income (loss)	288														288
Deferred compensation								(3)
Cash dividends declared on common shares									(172)
Cash dividends declared on preferred stock										$ (6)	$ (8)	$ (6)
Open market common share repurchases (in shares)							9,968,000
Open market Common Share repurchases														(167)
Employee equity compensation program Common Share repurchases (in shares)							1,823,000
Employee equity compensation program Common Share repurchases								(2)						(32)
Common shares reissued (returned) for stock options and other employee benefit plans, shares							5,474,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(67)						97
Net contribution from (distribution to) noncontrolling interests																1
Ending Balance, Preferred Shares (in shares) at Mar. 31, 2019						946,000
Ending Balance, Common Shares (in shares) at Mar. 31, 2019							1,013,186,000
Ending Balance at Mar. 31, 2019						$ 1,450	$ 1,257	6,259	11,771					(4,283)	(530)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						1,450	1,257	6,259	11,771					(4,283)	(530)	2
Beginning Balance	17,038					$ 1,900	$ 1,257	6,295	12,469					(4,909)	26	0
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2019						1,396,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2019							977,189,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	17,411					$ 1,900	$ 1,257	6,222	12,174					(4,956)	814	0
Net income (loss)	146								146							0
Other comprehensive income (loss)	788														788
Deferred compensation								(1)
Cash dividends declared on common shares									(181)
Cash dividends declared on preferred stock										$ (7)	$ (8)	$ (6)	$ (6)
Open market common share repurchases (in shares)							(6,067,000)
Open market Common Share repurchases														(117)
Employee equity compensation program Common Share repurchases (in shares)							(1,795,000)
Employee equity compensation program Common Share repurchases								(72)						(35)
Common shares reissued (returned) for stock options and other employee benefit plans, shares							5,992,000
Common Shares reissued (returned) for stock options and other employee benefit plans								0						105
Net contribution from (distribution to) noncontrolling interests																0
Ending Balance, Preferred Shares (in shares) at Mar. 31, 2020		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Mar. 31, 2020							975,319,000
Ending Balance at Mar. 31, 2020	17,411					$ 1,900	$ 1,257	6,222	12,174					(4,956)	814	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 17,411					$ 1,900	$ 1,257	$ 6,222	$ 12,174					$ (4,956)	$ 814	$ 0