Benefit Plans (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Reclassification of prior service cost to net periodic pension benefit cost	$ 7,710	$ 3,590	$ 1,138
Amount recognized in other comprehensive income	(54,366)	3,201	(17,367)
Assumed Healthcare Cost Trend Rates at December 31
Healthcare cost trend rate assumed for next year	7.50%
Rate to which the cost trend rate gradually declines	5.00%
Year that the rate reaches the rate it is assumed to maintain	2017
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Expected return on plan assets	8.00%	8.00%	8.25%
Pension Plans [Member]
Components of Net Periodic Benefit Cost
Service cost	20,762	19,217	18,638
Interest cost	42,383	41,621	41,941
Expected return on plan assets	(49,480)	(50,122)	(46,505)
Amortization of prior service cost (credit)	340	460	460
Amortization of actuarial loss	11,670	5,752	1,651
Net periodic pension benefit cost	25,675	16,928	16,185
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)	90,886	(17,413)	27,811
Reclassification of actuarial loss to net periodic pension benefit cost	(11,670)	(5,752)	(1,651)
Reclassification of prior service cost to net periodic pension benefit cost	(340)	(460)	(460)
Amount recognized in other comprehensive income	78,876	(23,625)	25,700
Amount recognized in net periodic pension benefit cost and other comprehensive income	104,551	(6,697)	41,885
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate	5.49%	5.92%	6.60%
Expected return on plan assets	8.00%	8.25%	8.25%
Rate of compensation increase (for salary-related plans)	3.50%	3.40%	4.75%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	4.96%	5.49%	5.92%
Rate of compensation increase (for salary-related plans)	3.50%	3.50%	3.40%
Postretirement Plans [Member]
Components of Net Periodic Benefit Cost
Service cost	4,789	4,265	3,912
Interest cost	6,450	6,651	7,045
Amortization of prior service cost (credit)	(674)	(728)	(823)
Amortization of actuarial loss	1,149	887	598
Net periodic pension benefit cost	11,714	11,075	10,732
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)	(2,853)	11,730	974
Reclassification of actuarial loss to net periodic pension benefit cost	(1,149)	(887)	(598)
Reclassification of prior service cost to net periodic pension benefit cost	674	728	823
Amount recognized in other comprehensive income	(3,328)	11,571	1,199
Amount recognized in net periodic pension benefit cost and other comprehensive income	$ 8,386	$ 22,646	$ 11,931
Assumed Healthcare Cost Trend Rates at December 31
Healthcare cost trend rate assumed for next year	7.50%	8.00%	8.50%
Rate to which the cost trend rate gradually declines	5.00%	5.00%	5.00%
Year that the rate reaches the rate it is assumed to maintain	2017	2017	2017
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate	4.95%	5.45%	6.65%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	4.60%	4.95%	5.45%