Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps) (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) month	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) month	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Interest Rate Swaps Linked to Overnight Index Swap Rate	79.00%			79.00%		86.00%
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (237)		$ (1,437)	$ (3,417)	$ (2,433)
Interest Rate Swaps Linked to 3-Month LIBOR	5.00%			5.00%		11.00%
Interest Rate Swaps Linked to Secured Overnight Financing Rate	16.00%			16.00%		3.00%
Interest Rate Swaption [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (14)		(25)	$ (148)	(52)
Notional Amount	$ 9,350			$ 9,350		$ 8,850
Average Fixed Pay Rate	2.22%			2.22%		2.34%
Options At Cost		$ 176		$ 175
Interest Rate Derivatives, at Fair Value, Net	$ 6			$ 6		$ 126
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month		11		7
Average Maturity (Years)		9 years 6 months		9 years 6 months
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(379)		$ (1,019)	$ (3,174)	$ (1,615)
Notional Amount	$ 42,075			$ 42,075		$ 79,075
Average Fixed Pay Rate	0.39%			0.39%		1.29%
Average Receive Rate	0.13%			0.13%		1.59%
Average Maturity (Years)		2 years 8 months 12 days		5 years 1 month 6 days
Less Than or Equal to One Year [Member] | Interest Rate Swaption [Member]
Notional Amount	$ 7,850			$ 7,850		$ 5,650
Average Fixed Pay Rate	2.29%			2.29%		2.26%
Options At Cost		$ 123		$ 150
Interest Rate Derivatives, at Fair Value, Net	$ 2			$ 2		$ 80
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month		8		6
Average Maturity (Years)		9 years 3 months 18 days		9 years 4 months 24 days
Greater Than One Year and Less Than or Equal to Two Years [Member] | Interest Rate Swaption [Member]
Notional Amount	$ 1,500			$ 1,500		$ 3,200
Average Fixed Pay Rate	1.85%			1.85%		2.50%
Options At Cost		$ 53		$ 25
Interest Rate Derivatives, at Fair Value, Net	$ 4			$ 4		$ 46
Cash Flow Hedges Derivative Instruments Not Designated As Hedging Instruments Average Months To Expiration | month		16		16
Average Maturity (Years)		10 years		10 years
Greater Than One Year and Less Than or Equal to Three Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 8,500			$ 8,500		$ 59,700
Average Fixed Pay Rate	0.24%			0.24%		1.30%
Average Receive Rate	0.21%			0.21%		1.58%
Average Maturity (Years)		1 year 7 months 6 days		2 years 4 months 24 days
Greater Than Three Years and Less Than or Equal to Five Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 16,500			$ 16,500		$ 9,850
Average Fixed Pay Rate	0.20%			0.20%		1.17%
Average Receive Rate	0.08%			0.08%		1.55%
Average Maturity (Years)		3 years 9 months 18 days		4 years 3 months 18 days
Greater Than Five Years and Less than or Equal to Seven Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 12,950			$ 12,950		$ 5,650
Average Fixed Pay Rate	0.56%			0.56%		1.34%
Average Receive Rate	0.14%			0.14%		1.70%
Average Maturity (Years)		6 years 4 months 24 days		6 years 2 months 12 days
Greater Than Seven Years and Less than or Equal to Ten Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 3,150			$ 3,150		$ 2,850
Average Fixed Pay Rate	0.78%			0.78%		1.36%
Average Receive Rate	0.08%			0.08%		1.58%
Average Maturity (Years)		8 years 10 months 24 days		8 years 7 months 6 days
Greater Than Ten Years [Member] | Interest Rate Swap [Member]
Notional Amount	$ 975			$ 975		$ 1,025
Average Fixed Pay Rate	1.30%			1.30%		1.64%
Average Receive Rate	0.16%			0.16%		1.78%
Average Maturity (Years)		15 years 4 months 24 days		15 years 8 months 12 days