Supplemental Information (Derivatives and Hedging - Cash Flow Hedges) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Summary Of Cash Flow Hedge Activity [Line Items]
Gain (loss) recognized in AOCI	$ (274)	$ (913)
Gain (loss) reclassified from AOCI into earnings	(364)	$ (918)
Pre-tax gain (loss) included in AOCI related to cash flow hedges of forecasted transactions	40
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 83
Maximum term of hedged forecasted transactions	16 years	17 years
Cash Flow Hedges [Member]
Summary Of Cash Flow Hedge Activity [Line Items]
Gain (loss) recognized in AOCI	$ (274)	$ (913)
Gain (loss) reclassified from AOCI into earnings	(364)	(918)
Interest Rate Contracts
Summary Of Cash Flow Hedge Activity [Line Items]
Gain (loss) recognized in AOCI	6	(1)
Gain (loss) reclassified from AOCI into earnings	(79)	(130)
Currency Exchange Contracts
Summary Of Cash Flow Hedge Activity [Line Items]
Gain (loss) recognized in AOCI	(281)	(907)
Gain (loss) reclassified from AOCI into earnings	(282)	(784)
Commodity Contracts
Summary Of Cash Flow Hedge Activity [Line Items]
Gain (loss) recognized in AOCI	0	(5)
Gain (loss) reclassified from AOCI into earnings	$ (2)	$ (4)