Derivative and Other Hedging Instruments (Summary Of Outstanding Forward Contracts Designated As Hedging Instruments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Purchases Of TBAs And Forward Settling Agency Securities [Member]	Dec. 31, 2010 Purchases Of TBAs And Forward Settling Agency Securities [Member]
Net Periodic Interest Rate Costs on Swaps	$ 457	$ (89)
Beginning Notional Amount			245	0
Additions			0	742
Settlement /Expirations			(245)	(497)
Ending Notional Amount			0	245
Fair Value as of Period End			0	(3)
Average Maturity as of Period End (Months)			0	0
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 252	$ 35