CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, at Cost	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2018		1,000,000	466,000,000
Beginning balance at Dec. 31, 2018	$ 20,817	$ 840	$ 6	$ 18,815	$ 5,385	$ (3,133)	$ (1,096)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(149)				(149)
Dividends to preferred stockholders	(15)				(15)
Preferred stock issued (in shares)		0
Preferred stock issued	292	$ 292
Treasury stock purchased (in shares)			(6,000,000)
Treasury stock purchased	(200)					(200)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	28			28		0
Employee stock purchase plan shares purchased	4			4
Total comprehensive income:
Net income	439				439
Other comprehensive income	298						298
Total comprehensive income	737				439		298
Ending balance (in shares) at Mar. 31, 2019		1,000,000	461,000,000
Ending balance at Mar. 31, 2019	21,531	$ 1,132	$ 6	18,847	5,672	(3,333)	(793)
Beginning balance (in shares) at Dec. 31, 2019		2,000,000	433,000,000
Beginning balance at Dec. 31, 2019	22,201	$ 1,570	$ 6	18,891	6,498	(4,353)	(411)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(168)				(168)
Dividends to preferred stockholders	$ (22)				(22)
Treasury stock purchased (in shares)	(7,548,655)		(7,000,000)
Treasury stock purchased	$ (270)					(270)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	6			6		0
Employee stock purchase plan shares purchased	4			4
Total comprehensive income:
Net income	34				34
Other comprehensive income	496						496
Total comprehensive income	530				34		496
Ending balance (in shares) at Mar. 31, 2020		2,000,000	427,000,000
Ending balance at Mar. 31, 2020	$ 21,950	$ 1,570	$ 6	$ 18,901	$ 6,011	$ (4,623)	$ 85