Derivative and Other Hedging Instruments (Remaining Interest Rate Swap Term) (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)
Interest Rate Swaption [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	90	(66)	(3)
Cost	98	159
Fair Value	$ 37	$ 75
Average Months to Expiration | month	6	10
Derivative Liability, Notional Amount	$ 3,500	$ 6,650
Average Fixed Pay Rate	2.93%	2.72%
Average Maturity (Years)	7 years 4 months 24 days	8 years 10 months 24 days
Payer Swaption [Member]
Average Receive Rate (LIBOR)	3M	3M
Interest Rate Swap [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 140	$ 67	$ (397)
Derivative Liability, Notional Amount	$ 51,625	$ 43,700
Average Fixed Pay Rate	2.11%	1.74%
Average Maturity (Years)	5 years	4 years 6 months
Less Than or Equal to One Year [Member] | Interest Rate Swaption [Member]
Cost	$ 80	$ 118
Fair Value	$ 23	$ 46
Average Months to Expiration | month	4	7
Derivative Liability, Notional Amount	$ 3,000	$ 5,100
Average Fixed Pay Rate	2.96%	2.71%
Average Maturity (Years)	7 years	8 years 9 months 18 days
Less Than or Equal to One Year [Member] | Payer Swaption [Member]
Average Receive Rate (LIBOR)	3M	3M
Greater Than One Year and Less Than or Equal to Three Years [Member] | Interest Rate Swap [Member]
Derivative Liability, Notional Amount	$ 19,900	$ 21,025
Average Fixed Pay Rate	1.63%	1.40%
Average Maturity (Years)	1 year 3 months 18 days	1 year 6 months
Bermudan [Member] | Interest Rate Swaption [Member]
Derivative Liability, Notional Amount	$ 700
Interest Rate Swaps Excluding Forward Starting [Member] | Interest Rate Swap [Member]
Average Fixed Pay Rate	1.98%	1.68%