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			(68)
Stock-based compensation plans expense			77
Issuance of shares for warrant exercise			(65)		65
Net income	$ 572			572
Dividends declared on common stock				(252)
Treasury stock acquired					(975)
Issuance of shares under incentive and stock compensation plans					90
Net shares acquired related to employee incentive and stock compensation plans					36
Total other comprehensive income (loss)						922
Ending balance at Sep. 30, 2017	17,233	$ 4	5,191	13,434	(1,981)	585
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		19,281
Issuance of shares under incentive and stock compensation plans		2,078
Return of shares under incentive and stock compensation plans to treasury stock		718
Issuance of shares for warrant exercise		1,512
Common Shares Outstanding, at end of period at Sep. 30, 2017		357,540
Beginning balance at Jun. 30, 2017						494
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	234
Ending balance at Sep. 30, 2017	17,233	$ 4	5,191	13,434	(1,981)	585
Common Shares Outstanding, at end of period at Sep. 30, 2017		357,540
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			(92)
Stock-based compensation plans expense			105
Issuance of shares for warrant exercise			(7)		7
Net income	1,611			1,611
Dividends declared on common stock				(285)
Treasury stock acquired					0
Issuance of shares under incentive and stock compensation plans					109
Net shares acquired related to employee incentive and stock compensation plans					36
Total other comprehensive income (loss)						(2,177)
Ending balance at Sep. 30, 2018	12,729	$ 4	4,385	10,973	(1,114)	(1,519)
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		2,373
Return of shares under incentive and stock compensation plans to treasury stock		694
Issuance of shares for warrant exercise		162
Common Shares Outstanding, at end of period at Sep. 30, 2018		358,676
Beginning balance at Jun. 30, 2018						(1,353)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	432
Ending balance at Sep. 30, 2018	$ 12,729	$ 4	$ 4,385	$ 10,973	$ (1,114)	$ (1,519)
Common Shares Outstanding, at end of period at Sep. 30, 2018		358,676