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	(143)				(143)
Dividends to preferred stockholders	(7)				(7)
Treasury stock purchased (in shares)			(7,000,000)
Treasury stock purchased	(260)			25		(285)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	8			8		0
Employee stock purchase plan shares purchased	6			6
Total comprehensive income:
Net income	638				638
Other comprehensive loss	75						75
Total comprehensive income	713				638		75
Ending balance (in shares) at Jun. 30, 2017		0	506,000,000
Ending balance at Jun. 30, 2017	20,064	$ 247	$ 6	18,761	3,191	(1,548)	(593)
Beginning balance at Mar. 31, 2017							(683)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to preferred stockholders	(7)
Treasury stock purchased	(130)
Total comprehensive income:
Net income	318
Other comprehensive loss	90
Total comprehensive income	408
Ending balance (in shares) at Jun. 30, 2017		0	506,000,000
Ending balance at Jun. 30, 2017	20,064	$ 247	$ 6	18,761	3,191	(1,548)	(593)
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	(215)				(215)
Dividends to preferred stockholders	(7)				(7)
Preferred stock issued (in shares)		1,000,000
Preferred stock issued	$ 296	$ 296
Treasury stock purchased (in shares)	(7,486,165)		(8,000,000)
Treasury stock purchased	$ (325)			0		(325)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	18			18		0
Employee stock purchase plan shares purchased	7			7
Total comprehensive income:
Net income	813				813
Other comprehensive loss	(390)						(390)
Total comprehensive income	423				813		(390)
Ending balance (in shares) at Jun. 30, 2018		1,000,000	484,000,000
Ending balance at Jun. 30, 2018	20,467	$ 543	$ 6	18,806	4,755	(2,433)	(1,210)
Beginning balance at Mar. 31, 2018							(1,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to preferred stockholders	(7)
Treasury stock purchased	(150)
Total comprehensive income:
Net income	425
Other comprehensive loss	(65)
Total comprehensive income	360
Ending balance (in shares) at Jun. 30, 2018		1,000,000	484,000,000
Ending balance at Jun. 30, 2018	$ 20,467	$ 543	$ 6	$ 18,806	$ 4,755	$ (2,433)	$ (1,210)