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	(53)				(53)
Dividends to preferred stockholders	(7)				(7)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	2			2		0
Employee stock purchase plan shares purchased	3			3
Net income	223
Total comprehensive income:
Net income	223				223
Other comprehensive loss	151						151
Total comprehensive income	374				223		151
Ending balance (in shares) at Mar. 31, 2016		0	529,000,000
Ending balance at Mar. 31, 2016	19,965	$ 247	$ 6	18,730	2,076	(858)	(236)
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)	(3,398,478)		(3,000,000)
Treasury stock purchased	$ (130)			25		(155)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	1			1		0
Employee stock purchase plan shares purchased	3			3
Net income	320
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)