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, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017
Cumulative effect of ASU adoptions							$ (16.0)
Common Stock [Abstract]
Common Stock, Beginning Balance				$ 2,710.0
Retained Earnings, Beginning Balance				35,481.0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	$ (940.0)		$ (98.0)	(148.0)		$ (265.0)
Treasury Stock, Beginning Balance				6,904.0
Noncontrolling interests, Beginning Balance				72.0
Total Equity, Beginning Balance, Adjusted							47,569.0
Total Equity, Beginning Balance				47,585.0		46,854.0
Net income	1,400.0		1,126.0	3,995.0		3,297.0
Other comprehensive income (loss), net of tax	(320.0)		76.0	(1,118.0)		243.0
Dividends, Cash [Abstract]
Common				(1,159.0)		(904.0)
Preferred				(181.0)		(181.0)
Redemptions of noncontrolling interests						(1,000.0)
Common Stock Activity Net				10.0		10.0
Treasury stock activity				(1,898.0)		(1,670.0)
Other				(116.0)		(197.0)
Common Stock, Ending Balance	2,710.0			2,710.0
Retained Earnings, Ending Balance	38,080.0			38,080.0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(1,260.0)		(22.0)	(1,260.0)		(22.0)
Treasury Stock, Ending Balance	8,771.0			8,771.0
Noncontrolling interests, Ending Balance	44.0			44.0
Total Equity, Ending Balance	47,102.0		46,452.0	$ 47,102.0		$ 46,452.0
Cash dividends declared, Common, per share (in dollars per share)				$ 2.45		$ 1.85
Par value less than $.5 million at each date	$ 0.5	[1]	$ 0.5	$ 0.5	[1]	$ 0.5	0.5	[1]
Common Stock [Member]
Common Stock [Abstract]
Beginning Balance (in shares)				473.0		485.0
Treasury stock activity, shares				(11.0)		(9.0)
Ending Balance, (in shares)	462.0		476.0	462.0		476.0
Common Stock, Beginning Balance				$ 2,710.0		$ 2,709.0
Dividends, Cash [Abstract]
Common Stock Activity Net						1.0
Common Stock, Ending Balance	$ 2,710.0		$ 2,710.0	$ 2,710.0		$ 2,710.0
Common stock activity (less than .5 million shares)				0.5		0.5
Capital Surplus - Preferred Stock [Member]
Common Stock [Abstract]
Capital surplus - Preferred Stock, Beginning Balance				$ 3,985.0		$ 3,977.0
Dividends, Cash [Abstract]
Preferred stock discount accretion				3.0		5.0
Other				(6.0)
Capital surplus - Preferred Stock, Ending Balance	3,982.0		3,982.0	3,982.0		3,982.0
Capital Surplus - Common Stock and Other [Member]
Common Stock [Abstract]
Capital surplus - Common Stock, Beginning Balance				12,389.0		12,674.0
Dividends, Cash [Abstract]
Common Stock Activity Net				10.0		9.0
Treasury stock activity				(31.0)		(274.0)
Other				(51.0)		(48.0)
Capital surplus - Common Stock, Ending Balance	12,317.0		12,361.0	12,317.0		12,361.0
Retained Earnings [Member]
Cumulative effect of ASU adoptions							(22.0)
Common Stock [Abstract]
Retained Earnings, Beginning Balance				35,459.0		31,670.0
Net income				3,964.0		3,258.0
Dividends, Cash [Abstract]
Common				(1,159.0)		(904.0)
Preferred				(181.0)		(181.0)
Preferred stock discount accretion				(3.0)		(5.0)
Redemptions of noncontrolling interests						(19.0)
Retained Earnings, Ending Balance	38,080.0		33,819.0	38,080.0		33,819.0
Accumulated Other Comprehensive Income (Loss) [Member]
Cumulative effect of ASU adoptions							$ 6.0
Common Stock [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance				(142.0)		(265.0)
Other comprehensive income (loss), net of tax				(1,118.0)		243.0
Dividends, Cash [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(1,260.0)		(22.0)	(1,260.0)		(22.0)
Treasury Stock [Member]
Common Stock [Abstract]
Treasury Stock, Beginning Balance				(6,904.0)		(5,066.0)
Dividends, Cash [Abstract]
Treasury stock activity				(1,867.0)		(1,396.0)
Treasury Stock, Ending Balance	(8,771.0)		(6,462.0)	(8,771.0)		(6,462.0)
Noncontrolling Interest [Member]
Common Stock [Abstract]
Noncontrolling interests, Beginning Balance				72.0		1,155.0
Net income				31.0		39.0
Dividends, Cash [Abstract]
Redemptions of noncontrolling interests						(981.0)
Other				(59.0)		(149.0)
Noncontrolling interests, Ending Balance	$ 44.0		$ 64.0	$ 44.0		$ 64.0
As Previously Reported [Member] | Common Stock [Member]
Common Stock [Abstract]
Beginning Balance (in shares)				473.0
Common Stock, Beginning Balance				$ 2,710.0
As Previously Reported [Member] | Capital Surplus - Preferred Stock [Member]
Common Stock [Abstract]
Capital surplus - Preferred Stock, Beginning Balance				3,985.0
As Previously Reported [Member] | Capital Surplus - Common Stock and Other [Member]
Common Stock [Abstract]
Capital surplus - Common Stock, Beginning Balance				12,389.0
As Previously Reported [Member] | Retained Earnings [Member]
Common Stock [Abstract]
Retained Earnings, Beginning Balance				35,481.0
As Previously Reported [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Common Stock [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance				(148.0)
As Previously Reported [Member] | Treasury Stock [Member]
Common Stock [Abstract]
Treasury Stock, Beginning Balance				(6,904.0)
As Previously Reported [Member] | Noncontrolling Interest [Member]
Common Stock [Abstract]
Noncontrolling interests, Beginning Balance				$ 72.0

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