Servicing Activities (Schedule Of Sensitivity Analysis of Fair Value) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Servicing Activities [Abstract]
Weighted average life (in years)	5 years 5 months	4 years 7 months
Weighted average prepayment speed	10.30%	13.50%
Impact on fair value of 10% adverse change	$ (64)	$ (77)
Impact on fair value of 20% adverse change	(122)	(144)
Weighted average discount rate	9.30%	7.70%
Impact on fair value of 10% adverse change, discount rate	(42)	(10)
Impact on fair value of 20% adverse change, discount rate	$ (80)	$ (19)