Derivative Instruments (Textuals) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
(Gain) Loss On Interest Rate Derivative Instruments Not Designated As Hedging Instruments, Unrealized				$ 14
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net		0		2
Derivative Instruments (Textuals) [Abstract]
Maximum length of time hedging using interest rate derivative instruments			10 years
Derivative, Net Liability Position, Aggregate Fair Value	16		16
Collateral Already Posted, Aggregate Fair Value	7		7
Additional Collateral, Aggregate Fair Value	0		0
Cumulative cash flow hedge losses remaining in AOCI			178		242
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			49
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments	0	0	0	(14)
Interest Rate Derivative Liabilities, Fair Value on Settlement Date [Line Items]
(Gain) Loss on Interest Rate Derivative Instruments Not Designated as Hedging Instruments, realized				142
Interest Rate Swap [Member]
Derivative Instruments (Textuals) [Abstract]
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments				$ 156