Accumulated Other Comprehensive Loss (Reclassifications) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Gains (losses) on cash flow hedges
Revenues		$ 880,891	$ 958,450	$ 1,771,572	$ 1,895,947
Interest expense		(20,971)	(21,482)	(45,035)	(45,546)
Tax benefit		(52,351)	(46,335)	(102,898)	(54,371)
Net income		156,363	98,859	241,569	148,126
Pension and Postretirement Benefit Plans
Tax benefit		(3,614)	(3,613)	(7,781)	(7,254)
Reclassification out of Accumulated Other Comprehensive Loss
Gains (losses) on cash flow hedges
Revenues	[1]	(432)	(346)	(828)	(580)
Cost of sales	[1]	(190)	153	(585)	352
Interest expense	[1]	(507)	(507)	(1,014)	(1,014)
Total before tax	[1]	(1,129)	(700)	(2,427)	(1,242)
Tax benefit	[1]	436	269	938	479
Net income	[1]	(693)	(431)	(1,489)	(763)
Losses on available for sale securities
Unrealized losses	[1]	(18)	(505)	(42)	(852)
Tax benefit	[1]	7	186	16	314
Net of tax	[1]	(11)	(319)	(26)	(538)
Pension and Postretirement Benefit Plans
Transition credit	[1],[2]	3	3	5	5
Prior service costs	[1],[2]	(61)	(27)	(120)	(54)
Actuarial losses	[1],[2]	(10,056)	(9,869)	(21,595)	(19,627)
Total before tax	[1],[2]	(10,114)	(9,893)	(21,710)	(19,676)
Tax benefit	[1],[2]	3,614	3,613	7,781	7,254
Net of tax	[1],[2]	$ (6,500)	$ (6,280)	$ (13,929)	$ (12,422)

[1] Amounts in parentheses indicate debits (reductions) to income.

[2] These items are included in the computation of net periodic costs of defined benefit pension plans and nonpension postretirement benefit plans (see Note 12 for additional details).