Derivative Financial Instruments (Derivative Instruments With Credit Risk-Related Contingent Features) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Derivative Financial Instruments [Abstract]
Aggregate Fair Value of Derivative Liabilities	$ 490	[1]	$ 456	[1]
Cash Collateral Posted	129		116
Potential Aggregate Amount of Additional Collateral Required	$ 380	[2]	$ 332	[2]

[1] Prior to consideration of master trading and netting agreements and including NPNS contract exposures.

[2] As collateral requirements with certain counterparties are based on master trading and netting agreements, the aggregate amount of additional collateral required to be posted is after consideration of the effects of such agreements.