Derivative Instruments and Other Financial Instruments Used For Hedging - Notional Amounts, Balance Sheet Location, and Fair Value Amounts of Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative notional amount	$ 63,201	$ 53,628
Asset Derivatives, Fair Value	1,548	1,350
Liability Derivatives, Fair Value	1,407	1,308
Designated as Hedging Instrument [Member] | Interest rate derivative contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	11,500	7,400
Asset Derivatives, Fair Value	53	3
Liability Derivatives, Fair Value		10
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	51,701	46,228
Asset Derivatives, Fair Value	1,495	1,347
Liability Derivatives, Fair Value	1,407	1,298
Not Designated as Hedging Instrument [Member] | Interest rate derivative contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	37,177	33,903
Asset Derivatives, Fair Value	1,084	922
Liability Derivatives, Fair Value	1,027	869
Not Designated as Hedging Instrument [Member] | Commodity derivative contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	5,761	5,136
Asset Derivatives, Fair Value	201	250
Liability Derivatives, Fair Value	170	247
Not Designated as Hedging Instrument [Member] | Foreign exchange derivative contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	5,237	4,152
Asset Derivatives, Fair Value	94	88
Liability Derivatives, Fair Value	95	95
Not Designated as Hedging Instrument [Member] | Equity derivative contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	3,491	3,037
Asset Derivatives, Fair Value	115	87
Liability Derivatives, Fair Value	115	87
Not Designated as Hedging Instrument [Member] | Other contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative notional amount	35
Asset Derivatives, Fair Value	$ 1