Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	$ (119,965)	$ (114,794)	$ (371,825)	$ (360,784)
Reclassification adjustments	(11,913)	(10,229)	(33,607)	(31,410)
Total before tax	(29,435)	(32,772)	(82,003)	(88,614)
Reclassification out of Accumulated Other Comprehensive Income | Pension and other postretirement plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of service cost	915	1,215	2,820	3,605
Total before tax	915	1,215	2,820	3,605
Total before tax	(321)	(397)	(964)	(1,187)
Total net of tax	594	818	1,856	2,418
Reclassification out of Accumulated Other Comprehensive Income | Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1,701	1,748	5,144	5,287
Reclassification adjustments	1,701	1,748	5,144	5,287
Total before tax	(619)	(634)	(1,872)	(1,917)
Total net of tax	$ 1,082	$ 1,114	$ 3,272	$ 3,370