Share Acitivity within Common, Preferred and Treasury Stock (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Values
Beginning Balance	$ 14,626	$ 13,764	$ 13,251
Shares acquired for treasury	(654)	(1,320)	(650)
Issuance of preferred stock	297	1,034
Issuance of preferred shares	297	1,034
Impact of stock transactions under stock compensation plans, net	60	60	43
Other		(1)	1
Ending Balance	15,665	14,626	13,764
Series J Preferred Stock
Values
Issuance of preferred shares	297
Series I Preferred Stock
Values
Issuance of preferred shares		441
Series H Preferred Stock
Values
Issuance of preferred shares		593
Series G Preferred Stock
Shares
Redemption of preferred shares, Series G		16,442
Common Stock
Values
Beginning Balance				2,051
Ending Balance	2,051	2,051	2,051	2,051
Shares
Beginning balance				923,892,581
Ending balance	923,892,581	923,892,581	923,892,581	923,892,581
Preferred Stock
Values
Beginning Balance		398		398
Issuance of preferred stock		1,034
Redemption of preferred shares, Series G		(398)
Ending Balance	1,331	1,034		398
Shares
Beginning balance		16,450		16,450
Redemption of preferred shares, Series G		(16,450)
Ending balance	54,000	42,000		16,450
Preferred Stock | Series J Preferred Stock
Shares
Issuance of preferred stock	12,000
Preferred Stock | Series I Preferred Stock
Shares
Issuance of preferred stock		18,000
Preferred Stock | Series H Preferred Stock
Shares
Issuance of preferred stock		24,000
Treasury Stock
Values
Beginning Balance	(1,295)	(634)	(64)
Shares acquired for treasury	(726)	(1,242)	(627)
Redemption of preferred shares, Series G		540
Impact of stock transactions under stock compensation plans, net	47	38	54
Other	2	3	3
Ending Balance	$ (1,972)	$ (1,295)	$ (634)
Shares
Beginning balance	68,586,836	41,740,524	4,088,145
Shares acquired for treasury	34,799,873	65,516,126	42,424,014
Redemption of preferred shares, Series G		(35,529,018)
Impact of stock transactions under stock compensation plans, net	(3,493,671)	(3,697,042)	(4,654,165)
Other	(47,409)	556,246	(117,470)
Ending balance	99,845,629	68,586,836	41,740,524