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)	Cumulative Effect, Period Of Adoption, Adjustment	Cumulative Effect, Period Of Adoption, Adjustment Retained Earnings	Cumulative Effect, Period Of Adoption, Adjustment 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)			$ 5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(459)				(459)
Dividends to preferred stockholders	(50)				(50)
Preferred stock issued (in shares)		0
Preferred stock issued	293	$ 293
Treasury stock purchased (in shares)			(23,000,000)
Treasury stock purchased	(820)					(820)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	48			48		0
Employee stock purchase plan shares purchased	13			13
Total comprehensive income:
Net income	1,341				1,341
Other comprehensive income	651						651
Total comprehensive income	1,992				1,341		651
Ending balance (in shares) at Sep. 30, 2019		1,000,000	444,000,000
Ending balance at Sep. 30, 2019	21,851	$ 1,133	$ 6	18,876	6,229	(3,953)	(440)	$ 17	$ 12	5
Beginning balance (in shares) at Jun. 30, 2019		1,000,000	458,000,000
Beginning balance at Jun. 30, 2019	22,017	$ 1,133	$ 6	18,860	5,959	(3,453)	(488)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(162)				(162)
Dividends to preferred stockholders	(17)				(17)
Treasury stock purchased (in shares)			(14,000,000)
Treasury stock purchased	(500)					(500)
Share-based compensation plans (in shares)			0
Share-based compensation plans	11			11		0
Employee stock purchase plan shares purchased	5			5
Total comprehensive income:
Net income	449				449
Other comprehensive income	48						48
Total comprehensive income	497				449		48
Ending balance (in shares) at Sep. 30, 2019		1,000,000	444,000,000
Ending balance at Sep. 30, 2019	21,851	$ 1,133	$ 6	18,876	6,229	(3,953)	(440)	17	12	5
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	(504)				(504)
Dividends to preferred stockholders	(75)				(75)
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	17			17		0
Employee stock purchase plan shares purchased	14			14
Total comprehensive income:
Net income	601				601
Other comprehensive income	421						421
Total comprehensive income	1,022				601		421
Ending balance (in shares) at Sep. 30, 2020		2,000,000	427,000,000
Ending balance at Sep. 30, 2020	22,469	$ 1,965	$ 6	18,922	6,189	(4,623)	10	(331)	(331)	0
Beginning balance (in shares) at Jun. 30, 2020		2,000,000	427,000,000
Beginning balance at Jun. 30, 2020	22,418	$ 1,965	$ 6	18,908	6,068	(4,623)	94
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(168)				(168)
Dividends to preferred stockholders	(25)				(25)
Preferred stock issued (in shares)		0
Preferred stock issued	0	$ 0
Treasury stock purchased (in shares)			0
Treasury stock purchased	0					0
Share-based compensation plans (in shares)			0
Share-based compensation plans	10			10		0
Employee stock purchase plan shares purchased	4			4
Total comprehensive income:
Net income	314				314
Other comprehensive income	(84)						(84)
Total comprehensive income	230				314		(84)
Ending balance (in shares) at Sep. 30, 2020		2,000,000	427,000,000
Ending balance at Sep. 30, 2020	$ 22,469	$ 1,965	$ 6	$ 18,922	$ 6,189	$ (4,623)	$ 10	$ (331)	$ (331)	$ 0