Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps Agreements Designated As Hedges in the Future) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value		$ 11
Average Months to Expiration		7
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments		3,200
Pay Rate		3.41%
Receive Rate		1M / 3M LIBOR
Term (Years)		7 years 8 months 12 days
Payer Swaption [Member]
Cost	274
Fair Value	171
Average Months to Expiration	21
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	14,450
Pay Rate	2.99%
Receive Rate	1M / 3M LIBOR
Term (Years)	7 years 9 months 12 days
Less Than or Equal to One Year [Member] | Payer Swaption [Member]
Cost	76	22
Fair Value	15	4
Average Months to Expiration	4	4
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	5,150	2,200
Pay Rate	2.65%	3.13%
Receive Rate	1M / 3M LIBOR	1M / 3M LIBOR
Term (Years)	8 years 6 months 24 days	6.5
Greater Than One Year and Less Than or Equal to Three Years [Member]
Cost		49
Greater Than One Year and Less Than or Equal to Three Years [Member] | Payer Swaption [Member]
Cost	65	27
Fair Value	34	7
Average Months to Expiration	19	15
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	4,050	1,000
Pay Rate	2.82%	4.04%
Receive Rate	3M LIBOR	1M / 3M LIBOR
Term (Years)	6 years 8 months	10 years 2 months
greater than two years less than or equal to three years [Member] | Payer Swaption [Member]
Cost	97
Fair Value	87
Average Months to Expiration	33
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	3,900
Pay Rate	3.51%
Receive Rate	3M LIBOR
Term (Years)	8 years 6 months 24 days
greater than three years less than or equal to four years [Member] | Payer Swaption [Member]
Cost	12
Fair Value	11
Average Months to Expiration	46
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	450
Pay Rate	3.20%
Receive Rate	3M LIBOR
Term (Years)	6 years 1 month 12 days
greater than four years less than or equal to five years [Member] | Payer Swaption [Member]
Cost	24
Fair Value	24
Average Months to Expiration	59
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	$ 900
Pay Rate	3.33%
Receive Rate	3M LIBOR
Term (Years)	5 years 0 months