Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change net of income taxes				$ 0		$ 0
Adjusted balance, beginning of period				13,114		(337)
Beginning balance at Dec. 31, 2016			$ 5,247	13,114	$ (1,125)	(337)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans			(65)
Stock-based compensation plans expense			56
Issuance of shares for warrant exercise			(43)		43
Net income	$ 338			338
Dividends declared on common stock				(170)
Treasury stock acquired					(650)
Issuance of shares under incentive and stock compensation plans					79
Net shares acquired related to employee incentive and stock compensation plans					34
Total other comprehensive income (loss)						831
Ending balance at Jun. 30, 2017	17,288	$ 4	5,195	13,282	(1,687)	494
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2016		373,949
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Treasury stock acquired		13,299
Issuance of shares under incentive and stock compensation plans		1,850
Return of shares under incentive and stock compensation plans to treasury stock		686
Issuance of shares for warrant exercise		1,006
Common Shares Outstanding, at end of period at Jun. 30, 2017		362,820
Beginning balance at Mar. 31, 2017						(207)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(40)
Ending balance at Jun. 30, 2017	17,288	$ 4	5,195	13,282	(1,687)	494
Common Shares Outstanding, at end of period at Jun. 30, 2017		362,820
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change net of income taxes				5		(5)
Adjusted balance, beginning of period				9,647		658
Beginning balance at Dec. 31, 2017	13,494		4,379	9,642	(1,194)	663
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under incentive and stock compensation plans			(83)
Stock-based compensation plans expense			83
Issuance of shares for warrant exercise			(5)		5
Net income	1,179			1,179
Dividends declared on common stock				(177)
Treasury stock acquired					0
Issuance of shares under incentive and stock compensation plans					95
Net shares acquired related to employee incentive and stock compensation plans					34
Total other comprehensive income (loss)						(2,011)
Ending balance at Jun. 30, 2018	12,546	$ 4	4,374	10,649	(1,128)	(1,353)
Common Shares Outstanding, beginning of period (in thousands) at Dec. 31, 2017		356,835
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Treasury stock acquired		0
Issuance of shares under incentive and stock compensation plans		2,042
Return of shares under incentive and stock compensation plans to treasury stock		637
Issuance of shares for warrant exercise		119
Common Shares Outstanding, at end of period at Jun. 30, 2018		358,359
Beginning balance at Mar. 31, 2018						(239)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	582
Ending balance at Jun. 30, 2018	$ 12,546	$ 4	$ 4,374	$ 10,649	$ (1,128)	$ (1,353)
Common Shares Outstanding, at end of period at Jun. 30, 2018		358,359