Total Equity and Other Comprehensive Income (Rollforward of Total Equity) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016	[1]
Common Stock [Abstract]
Common Stock, Beginning Balance				$ 2,709
Retained Earnings, Beginning Balance				31,670
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	$ (98)		$ 736	(265)		$ 130
Treasury Stock, Beginning Balance				5,066
Noncontrolling interests, Beginning Balance				1,155
Total Equity, Beginning Balance				46,854		45,980
Net income	1,126		1,006	3,297		2,938
Other comprehensive income (loss), net of tax	76		(90)	243		516
Dividends, Cash [Abstract]
Common				(904)		(791)
Preferred				(181)		(168)
Redemption of noncontrolling interests				(1,000)
Common stock activity				10		11
Treasury stock activity				(1,670)		(1,420)
Other				(197)		(221)
Common Stock, Ending Balance	2,710			2,710
Retained Earnings, Ending Balance	33,819			33,819
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(22)		646	(22)		646
Treasury Stock, Ending Balance	6,462			6,462
Noncontrolling interests, Ending Balance	64			64
Total Equity, Ending Balance	46,452		46,845	$ 46,452		$ 46,845
Cash dividends declared, Common, per share (in dollars per share)				$ 1.85		$ 1.57
Par value less than $.5 million at each date		[1]			[1]
Common Stock [Member]
Common Stock [Abstract]
Beginning Balance (in shares)				485.0		504.0
Treasury stock activity, shares				(9.0)		(16.0)
Ending Balance, (in shares)	476.0		488.0	476.0		488.0
Common Stock, Beginning Balance				$ 2,709		$ 2,708
Dividends, Cash [Abstract]
Common stock activity				1		1
Common Stock, Ending Balance	$ 2,710		$ 2,709	$ 2,710		$ 2,709
Common stock activity (less than .5 million shares)				0.5		0.5
Preferred Stock Including Additional Paid in Capital [Member]
Common Stock [Abstract]
Capital surplus - Preferred Stock, Beginning Balance				$ 3,977		$ 3,452
Dividends, Cash [Abstract]
Preferred stock discount accretion				5		4
Capital surplus - Preferred Stock, Ending Balance	3,982		3,456	3,982		3,456
Common Stock Including Additional Paid in Capital [Member]
Common Stock [Abstract]
Capital surplus - Common Stock, Beginning Balance				12,674		12,745
Dividends, Cash [Abstract]
Common stock activity				9		10
Treasury stock activity				(274)		(23)
Other				(48)		(29)
Capital surplus - Common Stock, Ending Balance	12,361		12,703	12,361		12,703
Retained Earnings [Member]
Common Stock [Abstract]
Retained Earnings, Beginning Balance				31,670		29,043
Net income				3,258		2,878
Dividends, Cash [Abstract]
Common				(904)		(791)
Preferred				(181)		(168)
Preferred stock discount accretion				(5)		(4)
Redemption of noncontrolling interests				(19)
Retained Earnings, Ending Balance	33,819		30,958	33,819		30,958
Accumulated Other Comprehensive Income (Loss) [Member]
Common Stock [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance				(265)		130
Other comprehensive income (loss), net of tax				243		516
Dividends, Cash [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(22)		646	(22)		646
Treasury Stock [Member]
Common Stock [Abstract]
Treasury Stock, Beginning Balance				(5,066)		(3,368)
Dividends, Cash [Abstract]
Treasury stock activity				(1,396)		(1,397)
Treasury Stock, Ending Balance	(6,462)		(4,765)	(6,462)		(4,765)
Noncontrolling Interest [Member]
Common Stock [Abstract]
Noncontrolling interests, Beginning Balance				1,155		1,270
Net income				39		60
Dividends, Cash [Abstract]
Redemption of noncontrolling interests				(981)
Other				(149)		(192)
Noncontrolling interests, Ending Balance	$ 64		$ 1,138	$ 64		$ 1,138

[1] Par value less than $.5 million at each date.