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						$ 1,025	$ 1,257	$ 6,335	$ 10,335					$ (3,150)	$ (779)	$ 2
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2017						521,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2017							1,069,084,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,450	$ 1,257	6,315	11,262					(3,910)	(1,166)	2
Other amounts reclassified from AOCI, net of income taxes	$ (5)								5
Net income (loss)	1,382								1,382							0
Other comprehensive income (loss)	(387)														(387)
Deferred compensation								16
Cash dividends declared on common shares									(415)
Cash dividends declared on preferred stock										$ (20)	$ (23)
Issuance of Preferred Stock (in shares)						425,000
Shares issued						$ 425		(13)
Open market common share repurchases (in shares)							(38,806,000)
Open market Common Share repurchases														(820)
Employee equity compensation program Common Share repurchases (in shares)							(2,271,000)
Employee equity compensation program Common Share repurchases														(47)
Common shares reissued (returned) for stock options and other employee benefit plans, shares							6,280,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(23)						107
Ending Balance, Preferred Shares (in shares) at Sep. 30, 2018						946,000
Ending Balance, Common Shares (in shares) at Sep. 30, 2018							1,034,287,000
Ending Balance at Sep. 30, 2018						$ 1,450	$ 1,257	6,315	11,262					(3,910)	(1,166)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,025	$ 1,257	6,315	10,970					(3,382)	(1,085)	2
Beginning Balance, Preferred Shares (in shares) at Jun. 30, 2018						521,000
Beginning Balance, Common Shares (in shares) at Jun. 30, 2018							1,058,944,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,450	$ 1,257	6,315	11,262					(3,910)	(1,166)	2
Other amounts reclassified from AOCI, net of income taxes									0
Net income (loss)	482								482							0
Other comprehensive income (loss)	(81)														(81)
Deferred compensation								4
Cash dividends declared on common shares									(176)
Cash dividends declared on preferred stock										(7)	(7)
Issuance of Preferred Stock (in shares)						425,000
Shares issued						$ 425		(13)
Open market common share repurchases (in shares)							(25,368,000)
Open market Common Share repurchases														(541)
Employee equity compensation program Common Share repurchases (in shares)							(50,000)
Employee equity compensation program Common Share repurchases														(1)
Common shares reissued (returned) for stock options and other employee benefit plans, shares							761,000
Common Shares reissued (returned) for stock options and other employee benefit plans								9						14
Ending Balance, Preferred Shares (in shares) at Sep. 30, 2018						946,000
Ending Balance, Common Shares (in shares) at Sep. 30, 2018							1,034,287,000
Ending Balance at Sep. 30, 2018						$ 1,450	$ 1,257	6,315	11,262					(3,910)	(1,166)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						1,450	1,257	6,315	11,262					(3,910)	(1,166)	2
Beginning Balance	15,596					$ 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	17,116					$ 1,900	$ 1,257	6,287	12,209					(4,696)	159	0
Net income (loss)	1,248								1,248							0
Other comprehensive income (loss)	977														977
Deferred compensation								6
Cash dividends declared on common shares									(525)
Cash dividends declared on preferred stock										(20)	(23)	$ (18)	$ (9)
Issuance of Preferred Stock (in shares)						450,000
Shares issued						$ 450		(15)
Open market common share repurchases (in shares)							(35,400,000)
Open market Common Share repurchases														(594)
Employee equity compensation program Common Share repurchases (in shares)							(1,880,000)
Employee equity compensation program Common Share repurchases								(3)						(33)
Common shares reissued (returned) for stock options and other employee benefit plans, shares							6,315,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(32)						112
Net contribution from (distribution to) noncontrolling interests																(1)
Ending Balance, Preferred Shares (in shares) at Sep. 30, 2019		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Sep. 30, 2019							988,538,000
Ending Balance at Sep. 30, 2019	17,116					$ 1,900	$ 1,257	6,287	12,209					(4,696)	159	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,900	$ 1,257	6,266	12,005					(4,457)	(2)	2
Beginning Balance, Preferred Shares (in shares) at Jun. 30, 2019						1,396,000
Beginning Balance, Common Shares (in shares) at Jun. 30, 2019							1,003,114,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	17,116					$ 1,900	$ 1,257	6,287	12,209					(4,696)	159	0
Net income (loss)	416								416							0
Other comprehensive income (loss)	161														161
Deferred compensation								5
Cash dividends declared on common shares									(182)
Cash dividends declared on preferred stock										$ (7)	$ (8)	$ (6)	$ (9)
Open market common share repurchases (in shares)							(15,075,000)
Open market Common Share repurchases														(248)
Employee equity compensation program Common Share repurchases (in shares)							(2,000)
Employee equity compensation program Common Share repurchases								0						0
Common shares reissued (returned) for stock options and other employee benefit plans, shares							501,000
Common Shares reissued (returned) for stock options and other employee benefit plans								16						9
Net contribution from (distribution to) noncontrolling interests																0
Ending Balance, Preferred Shares (in shares) at Sep. 30, 2019		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Sep. 30, 2019							988,538,000
Ending Balance at Sep. 30, 2019	17,116					$ 1,900	$ 1,257	6,287	12,209					(4,696)	159	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 17,116					$ 1,900	$ 1,257	$ 6,287	$ 12,209					$ (4,696)	$ 159	$ 0