Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Series D Preferred Stock	Series E Preferred Stock	Series F Preferred Stock	Series G Preferred Stock	Preferred Stock	Common Stock	Capital Surplus	Retained Earnings	Retained Earnings Series D Preferred Stock	Retained Earnings Series E Preferred Stock	Retained Earnings Series F Preferred Stock	Retained Earnings Series G Preferred Stock	Treasury Stock, at Cost	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Cumulative Effect, Period of Adoption, Adjustment Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,900	$ 1,257	$ 6,295	$ 12,469					$ (4,909)	$ 26	$ 0	$ (230)
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]
Net income (loss)	$ 333								333
Other comprehensive income (loss)	910														910
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense								0
Cash dividends declared on common shares									(362)
Cash dividends declared on preferred stock										$ (13)	$ (15)	$ (12)	$ (13)
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)							(1,814,000)
Employee equity compensation program Common Share repurchases								(55)						(36)
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)							6,639,000
Common Shares reissued (returned) for stock options and other employee benefit plans														117
Net contribution from (distribution to) noncontrolling interests																0
Other									(3)
Ending Balance, Preferred Shares (in shares) at Jun. 30, 2020						1,396,000
Ending Balance, Common Shares (in shares) at Jun. 30, 2020							975,947,000
Ending Balance at Jun. 30, 2020						$ 1,900	$ 1,257	6,240	12,154					(4,945)	936	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,900	$ 1,257	6,222	12,174					(4,956)	814	0
Beginning Balance, Preferred Shares (in shares) at Mar. 31, 2020						1,396,000
Beginning Balance, Common Shares (in shares) at Mar. 31, 2020							975,319,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	187								187
Other comprehensive income (loss)	122
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense								1
Cash dividends declared on common shares									(181)						122
Cash dividends declared on preferred stock										(6)	(7)	(6)	(7)
Open market Common Share repurchases (in shares)							0
Open market Common Share repurchases														0
Employee equity compensation program Common Share repurchases (in shares)							(19,000)
Employee equity compensation program Common Share repurchases								17						(1)
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)							647,000
Common Shares reissued (returned) for stock options and other employee benefit plans								0						12
Net contribution from (distribution to) noncontrolling interests																0
Ending Balance, Preferred Shares (in shares) at Jun. 30, 2020						1,396,000
Ending Balance, Common Shares (in shares) at Jun. 30, 2020							975,947,000
Ending Balance at Jun. 30, 2020						$ 1,900	$ 1,257	6,240	12,154					(4,945)	936	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						1,900	1,257	6,240	12,154					(4,945)	936	0
Beginning Balance	17,981					$ 1,900	$ 1,257	6,281	12,751					(4,946)	738	0
Beginning Balance, Preferred Shares (in shares) at Dec. 31, 2020						1,396,000
Beginning Balance, Common Shares (in shares) at Dec. 31, 2020							975,773,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,351								1,351							0
Other comprehensive income (loss)	(588)														(588)
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense								0
Cash dividends declared on common shares									(360)
Cash dividends declared on preferred stock										(13)	(15)	(12)	(13)
Open market Common Share repurchases (in shares)							(20,979,000)
Open market Common Share repurchases														(435)
Employee equity compensation program Common Share repurchases (in shares)							(1,602,000)
Employee equity compensation program Common Share repurchases								0						(32)
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)							7,084,000
Common Shares reissued (returned) for stock options and other employee benefit plans								(49)						126
Net contribution from (distribution to) noncontrolling interests																0
Other									0
Ending Balance, Preferred Shares (in shares) at Jun. 30, 2021		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Jun. 30, 2021							960,276,000
Ending Balance at Jun. 30, 2021	17,941					$ 1,900	$ 1,257	6,232	13,689					(5,287)	150	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance						$ 1,900	$ 1,257	6,213	13,166					(5,005)	103	0
Beginning Balance, Preferred Shares (in shares) at Mar. 31, 2021						1,396,000
Beginning Balance, Common Shares (in shares) at Mar. 31, 2021							972,587,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	729								729
Other comprehensive income (loss)	47														47
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense								3
Cash dividends declared on common shares									(179)
Cash dividends declared on preferred stock										$ (6)	$ (8)	$ (6)	$ (7)
Open market Common Share repurchases (in shares)							(13,278,000)
Open market Common Share repurchases														(299)
Employee equity compensation program Common Share repurchases (in shares)							(26,000)
Employee equity compensation program Common Share repurchases								0						(1)
Common shares reissued (returned) for stock options and other employee benefit plans (in shares)							993,000
Common Shares reissued (returned) for stock options and other employee benefit plans								16						18
Ending Balance, Preferred Shares (in shares) at Jun. 30, 2021		21,000	500,000	425,000	450,000	1,396,000
Ending Balance, Common Shares (in shares) at Jun. 30, 2021							960,276,000
Ending Balance at Jun. 30, 2021	17,941					$ 1,900	$ 1,257	6,232	13,689					(5,287)	150	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 17,941					$ 1,900	$ 1,257	$ 6,232	$ 13,689					$ (5,287)	$ 150	$ 0