Common, Preferred and Treasury Stock (Share Acitivity within Common, Preferred and Treasury Stock) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2016
Values
Beginning Balance	$ 16,220	$ 16,224	$ 16,081	$ 15,870	$ 15,736
Shares acquired for treasury		(1,453)	(1,605)		(661)
Impact of stock transactions under stock compensation plans, net		65	67		80
Other		(22)	(6)		1
Ending Balance	16,250	16,250	16,220	16,081	16,081
Common stock
Values
Beginning Balance	2,051	2,051	2,051	2,051	2,051
Ending Balance	$ 2,051	$ 2,051	$ 2,051	$ 2,051	$ 2,051
Shares
Beginning balance	923,892,581		923,892,581	923,892,581
Ending balance	923,892,581	923,892,581	923,892,581	923,892,581	923,892,581
Preferred Stock
Values
Beginning Balance	$ 1,331	$ 1,331	$ 1,331	$ 1,331	$ 1,331
Ending Balance	$ 1,331	$ 1,331	$ 1,331	$ 1,331	$ 1,331
Shares
Beginning balance	54,000		54,000	54,000
Ending balance	54,000	54,000	54,000	54,000	54,000
Treasury Stock
Values
Beginning Balance	$ (5,002)	$ (5,002)	$ (3,433)	$ (2,764)	$ (2,764)
Shares acquired for treasury		(1,494)	(1,588)		(668)
Impact of stock transactions under stock compensation plans, net		23	16		(4)
Other		2	3		3
Ending Balance	$ (6,471)	$ (6,471)	$ (5,002)	$ (3,433)	$ (3,433)
Shares
Beginning balance	230,087,688		173,413,282	138,812,267
Shares acquired for treasury	49,967,134		58,493,506	34,633,221
Impact of stock transactions under stock compensation plans, net	(2,698,451)		(1,693,503)	42,357
Other	(94,647)		(125,597)	(74,563)
Ending balance	277,261,724	277,261,724	230,087,688	173,413,282	173,413,282