Derivative Assets And Liabilities (Interest Rate Swaps Outstanding) (Details) - Derivatives Not Designated As Hedging Instruments - Interest Rate Derivatives [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
March 2019 [Member]
Notional Amount		$ 0	$ 300
Type	[1]	Pay a floating rate and receive a fixed rate of 1.42%
July 2019 [Member] | Forward-Starting Swaps [Member]
Notional Amount	[2],[3]	$ 400	400
Type	[1],[2],[3]	Forward-starting to pay a fixed rate of 3.52% and receive a floating rate
July 2021 [Member] | Forward-Starting Swaps [Member]
Notional Amount	[3]	$ 400	400
Type	[1],[3]	Forward-starting to pay a fixed rate of 3.55% and receive a floating rate
July 2018 [Member] | Forward-Starting Swaps [Member]
Notional Amount	[3]	$ 0	400
Type	[1],[3]	Forward-starting to pay a fixed rate of 3.56% and receive a floating rate
July 2022 [Member] | Forward-Starting Swaps [Member]
Notional Amount	[3]	$ 400	$ 0
Type	[1],[3]	Forward-starting to pay a fixed rate of 3.80% and receive a floating rate

[1] Floating rates are based on 3-month LIBOR.

[2] The July 2020 interest rate swaps were terminated in January 2020.

[3] Represents the effective date. These forward-starting swaps have terms of 30 years with a mandatory termination date the same as the effective date.