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	(117)				(117)
Dividends to preferred stockholders	(7)				(7)
Share-based compensation plans (in shares)			1,000,000
Share-based compensation plans	5			5		0
Employee stock purchase plan shares purchased	5			5
Total comprehensive income:
Net income	466				466
Other comprehensive income	228						228
Total comprehensive income	694				466		228
Ending balance (in shares) at Jun. 30, 2016		0	529,000,000
Ending balance at Jun. 30, 2016	20,226	$ 247	$ 6	18,735	2,255	(858)	(159)
Beginning balance at Mar. 31, 2016							(236)
Total comprehensive income:
Net income	243
Other comprehensive income	77
Total comprehensive income	320
Ending balance (in shares) at Jun. 30, 2016		0	529,000,000
Ending balance at Jun. 30, 2016	20,226	$ 247	$ 6	18,735	2,255	(858)	(159)
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)	(7,127,809)		(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 income	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]
Treasury stock purchased	(130)
Total comprehensive income:
Net income	318
Other comprehensive income	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)