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 Income (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	(297)				(297)
Dividends to preferred stockholders	(33)				(33)
Preferred stock issued (in shares)		0
Preferred stock issued	293	$ 293
Treasury stock purchased (in shares)			(9,000,000)
Treasury stock purchased	(320)					(320)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	37			37		0
Employee stock purchase plan shares purchased	8			8
Total comprehensive income:
Net income	892				892
Other comprehensive income	603						603
Total comprehensive income	1,495				892		603
Ending balance (in shares) at Jun. 30, 2019		1,000,000	458,000,000
Ending balance at Jun. 30, 2019	22,017	$ 1,133	$ 6	18,860	5,959	(3,453)	(488)
Beginning balance (in shares) at Mar. 31, 2019		1,000,000	461,000,000
Beginning balance at Mar. 31, 2019	21,531	$ 1,132	$ 6	18,847	5,672	(3,333)	(793)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(148)				(148)
Dividends to preferred stockholders	(18)				(18)
Preferred stock issued (in shares)		0
Preferred stock issued	1	$ 1
Treasury stock purchased (in shares)			(3,000,000)
Treasury stock purchased	(120)					(120)
Share-based compensation plans (in shares)			0
Share-based compensation plans	9			9		0
Employee stock purchase plan shares purchased	4			4
Total comprehensive income:
Net income	453				453
Other comprehensive income	305						305
Total comprehensive income	758				453		305
Ending balance (in shares) at Jun. 30, 2019		1,000,000	458,000,000
Ending balance at Jun. 30, 2019	22,017	$ 1,133	$ 6	18,860	5,959	(3,453)	(488)
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	(336)				(336)
Dividends to preferred stockholders	(50)				(50)
Preferred stock issued (in shares)		0
Preferred stock issued	$ 395	$ 395
Treasury stock purchased (in shares)	(7,548,655)		(7,000,000)
Treasury stock purchased	$ (270)			0		(270)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	7			7		0
Employee stock purchase plan shares purchased	10			10
Total comprehensive income:
Net income	287				287
Other comprehensive income	505						505
Total comprehensive income	792				287		505
Ending balance (in shares) at Jun. 30, 2020		2,000,000	427,000,000
Ending balance at Jun. 30, 2020	22,418	$ 1,965	$ 6	18,908	6,068	(4,623)	94
Beginning balance (in shares) at Mar. 31, 2020		2,000,000	427,000,000
Beginning balance at Mar. 31, 2020	21,950	$ 1,570	$ 6	18,901	6,011	(4,623)	85
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(168)				(168)
Dividends to preferred stockholders	(28)				(28)
Preferred stock issued (in shares)		0
Preferred stock issued	395	$ 395
Treasury stock purchased (in shares)			0
Treasury stock purchased	0					0
Share-based compensation plans (in shares)			0
Share-based compensation plans	1			1		0
Employee stock purchase plan shares purchased	6			6
Total comprehensive income:
Net income	253				253
Other comprehensive income	9						9
Total comprehensive income	262				253		9
Ending balance (in shares) at Jun. 30, 2020		2,000,000	427,000,000
Ending balance at Jun. 30, 2020	$ 22,418	$ 1,965	$ 6	$ 18,908	$ 6,068	$ (4,623)	$ 94