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 A Preferred Stock [Member]	Retained Earnings [Member] Series C Preferred Stock [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]
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2016						17,421,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2016							1,079,314,000
Beginning Balance at Dec. 31, 2016						$ 1,665	$ 1,257	$ 6,385	$ 9,378							$ (2,904)	$ (541)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 1,298								1,296									2
Other comprehensive income (loss)	(238)																(238)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate									141
Deferred compensation								16
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(410)
Cash dividends declared on preferred stock										$ (6)	$ (7)	$ (26)	$ (31)
Open market Common Share repurchases (in shares)							(36,140,000)
Open market Common Share repurchases																(665)
Employee equity compensation program Common Share repurchases (in shares)							(3,520,000)
Employee equity compensation program Common Share repurchases																(65)
Series A Preferred Stock exchanged for Common Shares (in shares)						(2,900,000)	20,568,000
Series A Preferred Stock exchanged for Common Shares						$ (290)		(49)								338
Redemption of Series C Preferred Stock (in shares)						(14,000,000)
Redemption of Series C Preferred Stock						$ (350)
Common Shares reissued (returned) for stock options and other employee benefit plans (in shares)							8,862,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(17)								146
Net contribution from (distribution to) noncontrolling interests																		0
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2017						521,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2017							1,069,084,000
Ending Balance at Dec. 31, 2017						$ 1,025	$ 1,257	6,335	10,335							(3,150)	(779)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other reclassification of AOCI									13
Net income (loss)	1,866								1,866									0
Other comprehensive income (loss)	(39)																(39)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	(13)
Deferred compensation								21
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(590)
Cash dividends declared on preferred stock												(26)	(31)	$ (9)
Issuance of Preferred Stock (in shares)						425,000
Issuance of Preferred Stock						$ 425		(13)
Open market Common Share repurchases (in shares)							(54,006,000)
Open market Common Share repurchases																(1,098)
Employee equity compensation program Common Share repurchases (in shares)							(2,286,000)
Employee equity compensation program Common Share repurchases																(47)
Common Shares reissued (returned) for stock options and other employee benefit plans (in shares)							6,711,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(12)								114
Net contribution from (distribution to) noncontrolling interests																		(1)
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2018						946,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2018							1,019,503,000
Ending Balance at Dec. 31, 2018	15,596					$ 1,450	$ 1,257	6,331	11,556							(4,181)	(818)	1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,717								1,717									0
Other comprehensive income (loss)	844																844
Deferred compensation								9
Dividends, Cash [Abstract]
Cash dividends declared on common shares									(707)
Cash dividends declared on preferred stock												$ (26)	$ (31)	$ (24)	$ (16)
Issuance of Preferred Stock (in shares)						450,000
Issuance of Preferred Stock						$ 450		(15)
Open market Common Share repurchases (in shares)							(48,347,000)
Open market Common Share repurchases																(835)
Employee equity compensation program Common Share repurchases (in shares)							(1,901,000)
Employee equity compensation program Common Share repurchases								(2)								(33)
Common Shares reissued (returned) for stock options and other employee benefit plans (in shares)							7,934,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(28)								140
Net contribution from (distribution to) noncontrolling interests																		(1)
Ending Balance, Preferred Shares (in shares) at Dec. 31, 2019		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Dec. 31, 2019							977,189,000
Ending Balance at Dec. 31, 2019	$ 17,038					$ 1,900	$ 1,257	$ 6,295	$ 12,469							$ (4,909)	$ 26	$ 0