Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative transactions entered into	$ 447	$ 158	$ 779	$ 499
Derivative transactions terminated	$ 391	$ 158	$ 712	$ 507