Employee Benefit Plans and Other Postretirement Benefits (Schedule Of Obligation And Funded Status) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets:
Prepaid benefit costs (long-term assets)	$ 0	$ 19,816,000
Pension and SERPA Benefits
Change in benefit obligation:
Benefit obligation, beginning of period	2,201,021,000	1,986,435,000
Service cost	32,340,000	31,584,000	$ 33,437,000
Interest cost	82,778,000	85,076,000	90,827,000
Actuarial (gains) losses	(213,583,000)	195,444,000
Plan participant contributions	0	0
Plan amendments	(12,926,000)	(13,227,000)
Benefits paid	(106,280,000)	(84,291,000)
Net curtailments and settlements	(1,358,000)	0
Benefit obligation, end of period	1,984,708,000	2,201,021,000	1,986,435,000
Change in plan assets:
Fair value of plan assets, beginning of period	2,162,885,000	1,899,889,000
Actual return on plan assets	(185,468,000)	320,144,000
Company contributions	0	25,000,000
Plan participant contributions	0	0
Benefits paid	102,799,000	82,148,000
Fair value of plan assets, end of period	1,874,618,000	2,162,885,000	1,899,889,000
Funded status of the plans, December 31	(110,090,000)	(38,136,000)
Prepaid benefit costs (long-term assets)	0	19,816,000
Accrued benefit liability (current liabilities)	(2,314,000)	(3,346,000)
Accrued benefit liability (long-term liabilities)	(107,776,000)	(54,606,000)
Net amount recognized	(110,090,000)	(38,136,000)
Postretirement Health Coverage
Change in benefit obligation:
Benefit obligation, beginning of period	338,488,000	346,431,000
Service cost	7,180,000	7,500,000	7,478,000
Interest cost	11,556,000	13,648,000	14,814,000
Actuarial (gains) losses	(42,039,000)	(8,408,000)
Plan participant contributions	2,492,000	2,525,000
Plan amendments	(4,710,000)	0
Benefits paid	(23,448,000)	(23,208,000)
Net curtailments and settlements	2,945,000	0
Benefit obligation, end of period	286,574,000	338,488,000	346,431,000
Change in plan assets:
Fair value of plan assets, beginning of period	217,537,000	170,092,000
Actual return on plan assets	(13,287,000)	32,445,000
Company contributions	0	15,000,000
Plan participant contributions	2,492,000	2,525,000
Benefits paid	16,385,000	2,525,000
Fair value of plan assets, end of period	190,357,000	217,537,000	$ 170,092,000
Funded status of the plans, December 31	(96,217,000)	(120,951,000)
Prepaid benefit costs (long-term assets)	0	0
Accrued benefit liability (current liabilities)	(1,764,000)	(2,198,000)
Accrued benefit liability (long-term liabilities)	(94,453,000)	(118,753,000)
Net amount recognized	$ (96,217,000)	$ (120,951,000)