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	(72)				(72)
Dividends to preferred stockholders	(7)				(7)
Treasury stock purchased (in shares)			(3,000,000)
Treasury stock purchased	(130)			25		(155)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	1			1
Employee stock purchase plan shares purchased	3			3
Total comprehensive income:
Net income	320				320
Other comprehensive loss	(15)						(15)
Total comprehensive income	305				320		(15)
Ending balance (in shares) at Mar. 31, 2017		0	510,000,000
Ending balance at Mar. 31, 2017	19,847	$ 247	$ 6	18,751	2,944	(1,418)	(683)
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	(108)				(108)
Dividends to preferred stockholders	$ (7)				(7)
Treasury stock purchased (in shares)	(3,887,023)		(4,000,000)
Treasury stock purchased	$ (175)					(175)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	13			13
Employee stock purchase plan shares purchased	3			3
Total comprehensive income:
Net income	388				388
Other comprehensive loss	(325)						(325)
Total comprehensive income	63				388		(325)
Ending balance (in shares) at Mar. 31, 2018		0	488,000,000
Ending balance at Mar. 31, 2018	$ 20,059	$ 247	$ 6	$ 18,797	$ 4,437	$ (2,283)	$ (1,145)