Consolidated Statements of Changes in Equity - USD ($) $ in Millions		Total	Series D Preferred Stock [Member]	Series E 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]	Treasury Stock, at Cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Beginning Balance, Preferred Shares at Dec. 31, 2016					17,421,000
Beginning Balance, Common 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)		$ 737						736							1
Other comprehensive income (loss)		35												35
Deferred compensation							7
Cash dividends declared on common shares								(194)
Cash dividends declared on preferred stock									$ (6)	$ (7)	$ (13)	$ (16)
Open market common share repurchases (in shares)						(10,602,000)
Open market Common Share repurchases													(196)
Employee equity compensation program common share repurchase (in shares)						(3,143,000)
Employee equity compensation program Common Share repurchases													(59)
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			$ 350
Common shares reissued (returned) for stock options and other employee benefit plans, shares						6,602,000
Series A Preferred Stock exchanged for Common Shares							(33)						110
Net contribution from (distribution to) noncontrolling interests															1
Ending Balance, Preferred Shares at Jun. 30, 2017					521,000
Ending Balance, Common Shares at Jun. 30, 2017						1,092,739,000
Ending Balance at Jun. 30, 2017					$ 1,025	$ 1,257	6,310	9,878					(2,711)	(506)	2
Beginning Balance at Mar. 31, 2017														(554)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		412
Other comprehensive income (loss)		48
Ending Balance, Preferred Shares at Jun. 30, 2017					521,000
Ending Balance, Common Shares at Jun. 30, 2017						1,092,739,000
Ending Balance at Jun. 30, 2017					$ 1,025	$ 1,257	6,310	9,878					(2,711)	(506)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect from changes in accounting principle	[1]							(2)
Beginning Balance, Preferred Shares at Dec. 31, 2017			21,000	500,000	521,000
Beginning Balance, Common Shares at Dec. 31, 2017						1,069,084,000
Beginning Balance at Dec. 31, 2017		15,025			$ 1,025	$ 1,257	6,335	10,335					(3,150)	(779)	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other reclassification of AOCI		(5)						5
Net income (loss)		900						900							0
Other comprehensive income (loss)		(306)												(306)
Deferred compensation							12
Cash dividends declared on common shares								(239)
Cash dividends declared on preferred stock											$ (13)	$ (16)
Open market common share repurchases (in shares)						(13,438,000)
Open market Common Share repurchases													(279)
Employee equity compensation program common share repurchase (in shares)						(2,221,000)
Employee equity compensation program Common Share repurchases													(46)
Redemption of Series C Preferred Stock		0
Common shares reissued (returned) for stock options and other employee benefit plans, shares						5,519,000
Series A Preferred Stock exchanged for Common Shares							(32)						93
Ending Balance, Preferred Shares at Jun. 30, 2018			21,000	500,000	521,000
Ending Balance, Common Shares at Jun. 30, 2018						1,058,944,000
Ending Balance at Jun. 30, 2018		15,102			$ 1,025	$ 1,257	6,315	10,970					(3,382)	(1,085)	2
Beginning Balance at Mar. 31, 2018														(991)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other reclassification of AOCI		(5)
Net income (loss)		482
Other comprehensive income (loss)		(94)
Ending Balance, Preferred Shares at Jun. 30, 2018			21,000	500,000	521,000
Ending Balance, Common Shares at Jun. 30, 2018						1,058,944,000
Ending Balance at Jun. 30, 2018		$ 15,102			$ 1,025	$ 1,257	$ 6,315	$ 10,970					$ (3,382)	$ (1,085)	$ 2

[1] Includes the impact of implementing ASU 2014-09, ASU 2016-01, and ASU 2017-12.