Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative transactions entered into	$ 472	$ 229	$ 1,251	$ 728
Derivative transactions terminated	$ 488	$ 166	$ 1,200	$ 673