Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) month	Dec. 31, 2017 USD ($) month	Dec. 31, 2016 USD ($)
Document Period End Date	Dec. 31, 2018
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (181)	$ 191	$ (323)
Payer Swaption [Member]
Interest Rate Derivative Not Designated As Hedging Instruments Receive Rate	3M	3M
Interest Rate Swaption [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 90	$ (66)	(3)
Notional Amount	$ 3,500	$ 6,650
Average Fixed Pay Rate	2.93%	2.72%
Options At Cost	$ 98	$ 159
Interest Rate Derivatives, at Fair Value, Net	$ 37	$ 75
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month	6	10
Average Maturity (Years)	7 years 4 months 24 days	8 years 10 months 24 days
Forward Contracts [Member] | Interest Rate Swap [Member]
Derivative, Notional Amount	$ 5,700	$ 4,600
Weighted Average Forward Start Date	6 months	3 months 18 days
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 140	$ 67	$ (397)
Notional Amount	$ 51,625	$ 43,700
Average Fixed Pay Rate	2.11%	1.74%
Average Receive Rate	2.63%	1.44%
Average Maturity (Years)	5 years	4 years 6 months
Less Than or Equal to One Year [Member] | Payer Swaption [Member]
Interest Rate Derivative Not Designated As Hedging Instruments Receive Rate	3M	3M
Less Than or Equal to One Year [Member] | Interest Rate Swaption [Member]
Notional Amount	$ 3,000	$ 5,100
Average Fixed Pay Rate	2.96%	2.71%
Options At Cost	$ 80	$ 118
Interest Rate Derivatives, at Fair Value, Net	$ 23	$ 46
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month	4	7
Average Maturity (Years)	7 years	8 years 9 months 18 days
Greater Than One Year and Less Than or Equal to Two Years [Member] | Payer Swaption [Member]
Interest Rate Derivative Not Designated As Hedging Instruments Receive Rate	3M	3M
Greater Than One Year and Less Than or Equal to Two Years [Member] | Interest Rate Swaption [Member]
Notional Amount	$ 500	$ 1,050
Average Fixed Pay Rate	2.78%	2.71%
Options At Cost	$ 18	$ 23
Interest Rate Derivatives, at Fair Value, Net	$ 14	$ 16
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month	18	18
Average Maturity (Years)	10 years	8 years 8 months 12 days
Greater Than Two Years and Less Than or Equal to Three Years [Member] | Payer Swaption [Member]
Interest Rate Derivative Not Designated As Hedging Instruments Receive Rate		3M
Greater Than Two Years and Less Than or Equal to Three Years [Member] | Interest Rate Swaption [Member]
Notional Amount		$ 500
Average Fixed Pay Rate		2.78%
Options At Cost		$ 18
Interest Rate Derivatives, at Fair Value, Net		$ 13
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month		30
Average Maturity (Years)		10 years
Greater Than One Year and Less Than or Equal to Three Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 19,900	$ 21,025
Average Fixed Pay Rate	1.63%	1.40%
Average Receive Rate	2.62%	1.46%
Average Maturity (Years)	1 year 3 months 18 days	1 year 6 months
Greater Than Three Years and Less Than or Equal to Five Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 8,425	$ 6,825
Average Fixed Pay Rate	2.06%	1.82%
Average Receive Rate	2.61%	1.43%
Average Maturity (Years)	4 years	4 years 1 month 6 days
Greater Than Five Years and Less than or Equal to Seven Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 7,875	$ 5,775
Average Fixed Pay Rate	2.66%	2.02%
Average Receive Rate	2.66%	1.44%
Average Maturity (Years)	6 years 1 month 6 days	5 years 10 months 24 days
Greater Than Seven Years and Less than or Equal to Ten Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 10,550	$ 6,650
Average Fixed Pay Rate	2.36%	2.10%
Average Receive Rate	2.64%	1.42%
Average Maturity (Years)	8 years 9 months 18 days	9 years 1 month 6 days
Greater Than Ten Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 4,875	$ 3,425
Average Fixed Pay Rate	2.77%	2.49%
Average Receive Rate	2.63%	1.45%
Average Maturity (Years)	11 years 7 months 6 days	12 years 10 months 24 days