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, 2015		0	528,000,000
Beginning balance at Dec. 31, 2015	$ 19,646	$ 247	$ 6	$ 18,725	$ 1,913	$ (858)	$ (387)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(179)				(179)
Dividends to preferred stockholders	(14)				(14)
Treasury stock purchased (in shares)			(11,000,000)
Treasury stock purchased	(250)					(250)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	8			8
Employee stock purchase plan shares purchased	7			7
Total comprehensive income:
Net income	763				763
Other comprehensive income	200						200
Total comprehensive income	963				763		200
Ending balance (in shares) at Sep. 30, 2016		0	518,000,000
Ending balance at Sep. 30, 2016	20,181	$ 247	$ 6	18,740	2,483	(1,108)	(187)
Beginning balance at Jun. 30, 2016							(159)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to preferred stockholders	(7)
Treasury stock purchased	(250)
Total comprehensive income:
Net income	297
Other comprehensive income	(28)
Total comprehensive income	269
Ending balance (in shares) at Sep. 30, 2016		0	518,000,000
Ending balance at Sep. 30, 2016	20,181	$ 247	$ 6	18,740	2,483	(1,108)	(187)
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)	(13,588,304)		(13,000,000)
Treasury stock purchased	$ (485)			25		(510)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	12			12
Employee stock purchase plan shares purchased	9			9
Total comprehensive income:
Net income	986				986
Other comprehensive income	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 income	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)