Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Gains (losses) on cash flow hedges
Revenues	$ 941,644		$ 920,489		$ 2,837,591		$ 2,780,514
Interest expense	(22,158)		(26,051)		(67,704)		(85,087)
Tax benefit	(25,310)		(10,032)		(79,681)		(52,045)
Net income (loss)	136,882		(933)		285,008		66,528
Pension and Postretirement Benefit Plans
Tax benefit	(3,355)		(4,347)		(10,609)		(15,613)
Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges
Revenues	429	[1]	(169)	[1]	1,009	[1]	(922)	[1]
Cost of sales	(42)	[1]	108	[1]	(394)	[1]	520	[1]
Interest expense	(507)	[1]	(507)	[1]	(1,521)	[1]	(1,521)	[1]
Total before tax	(120)	[1]	(568)	[1]	(906)	[1]	(1,923)	[1]
Tax benefit	(47)	[1]	(222)	[1]	(350)	[1]	(750)	[1]
Net income (loss)	(73)	[1]	(346)	[1]	(556)	[1]	(1,173)	[1]
Gains (losses) on available for sale securities
Interest income	(249)	[1]	1,640	[1]	(1,101)	[1]	(962)	[1]
Tax (benefit) provision	(92)	[1]	607	[1]	(406)	[1]	(356)	[1]
Net of tax	(157)	[1]	1,033	[1]	(695)	[1]	(606)	[1]
Pension and Postretirement Benefit Plans
Transition credit	3	[1],[2]	2	[1],[2]	8	[1],[2]	6	[1],[2]
Prior service costs	(27)	[1],[2]	(163)	[1],[2]	(81)	[1],[2]	(524)	[1],[2]
Actuarial losses	(10,025)	[1],[2]	(12,136)	[1],[2]	(29,652)	[1],[2]	(44,038)	[1],[2]
Total before tax	(10,049)	[1],[2]	(12,297)	[1],[2]	(29,725)	[1],[2]	(44,556)	[1],[2]
Tax benefit	(3,355)	[1],[2]	(4,347)	[1],[2]	(10,609)	[1],[2]	(15,613)	[1],[2]
Net of tax	$ (6,694)	[1],[2]	$ (7,950)	[1],[2]	$ (19,116)	[1],[2]	$ (28,943)	[1],[2]

[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 14 for additional details).