Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative transactions entered into	$ 224	$ 472	$ 2,271	$ 1,251
Derivative transactions terminated	$ 221	$ 488	$ 2,286	$ 1,200