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, 2016		0	512,000,000
Beginning balance at Dec. 31, 2016	$ 19,747	$ 247	$ 6	$ 18,722	$ 2,703	$ (1,263)	$ (668)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(233)				(233)
Dividends to preferred stockholders	(14)				(14)
Treasury stock purchased (in shares)			(13,000,000)
Treasury stock purchased	(485)			25		(510)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	12			12		0
Employee stock purchase plan shares purchased	9			9
Total comprehensive income:
Net income	986				986
Other comprehensive loss	87						87
Total comprehensive income	1,073				986		87
Ending balance (in shares) at Sep. 30, 2017		0	500,000,000
Ending balance at Sep. 30, 2017	20,109	$ 247	$ 6	18,768	3,442	(1,773)	(581)
Beginning balance at Jun. 30, 2017							(593)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to preferred stockholders	(7)
Treasury stock purchased	(225)
Total comprehensive income:
Net income	348
Other comprehensive loss	12
Total comprehensive income	360
Ending balance (in shares) at Sep. 30, 2017		0	500,000,000
Ending balance at Sep. 30, 2017	20,109	$ 247	$ 6	18,768	3,442	(1,773)	(581)
Beginning balance (in shares) at Dec. 31, 2017		0	491,000,000
Beginning balance at Dec. 31, 2017	20,270	$ 247	$ 6	18,781	4,164	(2,108)	(820)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(344)				(344)
Dividends to preferred stockholders	(14)				(14)
Preferred stock issued (in shares)		1,000,000
Preferred stock issued	$ 296	$ 296
Treasury stock purchased (in shares)	(17,527,586)		(18,000,000)
Treasury stock purchased	$ (725)			0		(725)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	24			24
Employee stock purchase plan shares purchased	11			11
Total comprehensive income:
Net income	1,256				1,256
Other comprehensive loss	(498)						(498)
Total comprehensive income	758				1,256		(498)
Ending balance (in shares) at Sep. 30, 2018		1,000,000	474,000,000
Ending balance at Sep. 30, 2018	20,276	$ 543	$ 6	18,816	5,062	(2,833)	(1,318)
Beginning balance at Jun. 30, 2018							(1,210)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to preferred stockholders	(7)
Treasury stock purchased	(400)
Total comprehensive income:
Net income	443
Other comprehensive loss	(108)
Total comprehensive income	335
Ending balance (in shares) at Sep. 30, 2018		1,000,000	474,000,000
Ending balance at Sep. 30, 2018	$ 20,276	$ 543	$ 6	$ 18,816	$ 5,062	$ (2,833)	$ (1,318)