Derivative Assets And Liabilities Outstanding Interest Rate Derivatives (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Dec. 31, 2019
July 2020 [Member]
Notional Amount	[1],[2]	$ 0	$ 400
Type	[1],[2],[3]	Forward-starting to pay a fixed rate of 3.52% and receive a floating rate
July 2021 [Member]
Notional Amount	[2]	$ 400	400
Type	[2],[3]	Forward-starting to pay a fixed rate of 3.55% and receive a floating rate
July 2022 [Member]
Notional Amount	[2]	$ 400	$ 400
Type	[2],[3]	Forward-starting to pay a fixed rate of 3.80% and receive a floating rate

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

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

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