Employee Benefit Plans (Schedule Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,448	$ 2,131
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	261	224
Equity Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	261	224
Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	750	646
Mutual Fund [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	750	646
Common collective trust funds - International equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	363	306
Common collective trust funds - U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	327	287
Debt instruments - Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	601	492
Debt instruments - Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	601	492
Debt instruments - U.S. Treasury instruments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	98	150
Debt instruments - U.S. Treasury instruments [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	98	150
Debt instruments - U.S. government agency, state and local government bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29	22
Debt instruments - U.S. government agency, state and local government bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29	22
Other Debt Instruments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	4
Other Debt Instruments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	4
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,758	1,538
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,109	1,020
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 649	$ 518