Retirement Plans (Details) (USD $)	1 Months Ended	6 Months Ended	9 Months Ended		12 Months Ended	1 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Aug. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Oct. 31, 2012 Pension Benefits [Member]	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2011 Pension Benefits [Member]	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2011 Pension Benefits [Member]	Sep. 30, 2012 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Sep. 30, 2011 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Sep. 30, 2012 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Sep. 30, 2011 Postretirement Benefits Other Than Pensions (OPEB) [Member]
Components of net periodic benefit cost [Abstract]
Service cost							$ 11,782,000	$ 9,615,000	$ 32,766,000	$ 28,844,000	$ 2,999,000	$ 4,206,000	$ 8,109,000	$ 12,662,000
Interest cost on projected benefit obligation							19,204,000	21,172,000	58,520,000	63,516,000	4,462,000	5,986,000	13,382,000	18,642,000
Expected return on plan assets							(23,655,000)	(25,589,000)	(71,833,000)	(76,766,000)	(19,000)	(79,000)	(129,000)	(242,000)
Amortization of prior service cost/(credit)							(50,000)	(50,000)	(150,000)	(150,000)	(2,545,000)	(2,552,000)	(7,551,000)	(7,651,000)
Amortization of unrecognized loss							6,845,000	4,435,000	22,419,000	13,306,000	1,830,000	607,000	5,652,000	3,604,000
Net periodic benefit cost							14,126,000	9,583,000	41,722,000	28,750,000	6,727,000	8,168,000	19,463,000	27,015,000
Total Net Contributions						10,300,000	18,200,000		28,500,000
Capitalization of pension and OPEB expense related to engineering and plant construction			11,700,000	9,800,000
Estimated pension and other postretirement benefit expenses, minimum			80,000,000
Estimated pension and other postretirement benefit expenses, maximum			85,000,000
Estimated pension and other postretirement benefit expenses					58,300,000
Number of pension plans merged with the pension plan			12
Fair value of plan assets for Acquired Business as of acquisition date	106,900,000	438,800,000	74,000,000
Plan assets			1,282,200,000		1,258,000,000
Increase in plan assets			24,200,000
Percentage of increase in pension plan assets (in hundredths)			2.00%
Positive investment returns related to increase in plan assets			147,500,000
Benefit payments			$ 123,300,000