Financial Derivatives (Risk Participation Agreements Sold) (Details) (Risk Participation Agreements Sold [Member], USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Risk Participation Agreements Sold [Member]
Notional Amount of Credit Risk Derivatives	$ 2,240	$ 2,053
Fair Value	$ (4)	$ (6)
Average term of credit risk derivatives	6 years 4 months	6 years 7 months