Derivative Financial Instruments (Schedule Of Open Interest Rate Swap Derivative Positions) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Interest Rate Contract 2.98% Expiration December 2048 [Member]
Derivative [Line Items]
Notional	$ 750
Rate Received	Three Month LIBOR
Rate Paid, percent	2.98%
Expiration	Dec. 31, 2018
Reference period end date	Dec. 31, 2048	[1]
Interest Rate Contract 1.76% Expiration January 2019 [Member]
Derivative [Line Items]
Notional	$ 100
Rate Received, percent	1.76%
Rate Paid	Three Month LIBOR
Expiration	Jan. 31, 2019

[1] Mandatory settlement in December 2018.