Retirement Plans (Schedule Of Expense Related To These Defined Contribution Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Expense related to defined contribution plans	$ 64	$ 79	$ 69
401(k) Plan And Enhanced Contribution Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Expense related to defined contribution plans	53	63	49
Canadian Pension And Savings Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Expense related to defined contribution plans	$ 11	$ 16	$ 20