Retirement Plans (Summary Of Reconciliation Of The Beginning And Ending Balances Of Assets Measured At Fair Value On A Recurring Basis Using Level 3 Inputs) (Details) - Guaranteed Deposit Account [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 11
Fair value of plan assets at end of year	9	$ 11
Defined benefit plan investment purchases	17	15
Purchases	(19)	(13)
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	11	9
Fair value of plan assets at end of year	9	11
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	11
Fair value of plan assets at end of year	$ 9	$ 11