Derivative Instruments - Impact on Statements of Income, Risk Management Derivatives (Details 2d) (Risk Management Activities [Member], Not Designated as Hedging Instrument, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Risk management derivatives gains and losses [Abstract]
Income statement impact	$ 462	$ 457
Interest rate contract
Risk management derivatives gains and losses [Abstract]
Income statement impact	458	536
Credit derivatives
Risk management derivatives gains and losses [Abstract]
Income statement impact	(31)	(74)
Foreign exchange
Risk management derivatives gains and losses [Abstract]
Income statement impact	1	5
Commodity
Risk management derivatives gains and losses [Abstract]
Income statement impact	$ 34	$ (10)