Derivative Instruments (Narratives) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Aggregate fair value of all derivatives with credit-risk-related contingent features that were in a net liability position	$ 2,700,000,000	$ 6,400,000,000
Fair value of collateral posted, aggregated	2,500,000,000	6,300,000,000
Additional collateral required or amount required to immediately settle our position if the credit-risk-related contingent features were triggered	$ 179,000,000	$ 159,000,000