Retirement Plans (Details) (USD $)	1 Months Ended	6 Months Ended			12 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Aug. 31, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2010	Dec. 31, 2011	Jun. 30, 2012 Maximum [Member]	Jun. 30, 2012 Minimum [Member]	Jun. 30, 2012 Pension Benefits [Member]	Jun. 30, 2011 Pension Benefits [Member]	Jun. 30, 2012 Pension Benefits [Member]	Jun. 30, 2011 Pension Benefits [Member]	Jun. 30, 2012 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Jun. 30, 2011 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Jun. 30, 2012 Postretirement Benefits Other Than Pensions (OPEB) [Member]	Jun. 30, 2011 Postretirement Benefits Other Than Pensions (OPEB) [Member]
Components of net periodic benefit cost [Abstract]
Service cost								$ 10,492,000	$ 9,615,000	$ 20,984,000	$ 19,230,000	$ 2,555,000	$ 4,228,000	$ 5,110,000	$ 8,456,000
Interest cost on projected benefit obligation								19,658,000	21,172,000	39,316,000	42,344,000	4,460,000	6,328,000	8,920,000	12,656,000
Expected return on plan assets								(24,089,000)	(25,589,000)	(48,178,000)	(51,178,000)	(55,000)	(82,000)	(110,000)	(164,000)
Amortization of prior service cost/(credit)								(50,000)	(50,000)	(100,000)	(100,000)	(2,503,000)	(2,550,000)	(5,006,000)	(5,100,000)
Amortization of unrecognized loss								7,787,000	4,435,000	15,574,000	8,870,000	1,911,000	1,499,000	3,822,000	2,998,000
Net periodic benefit cost								13,798,000	9,583,000	27,596,000	19,166,000	6,368,000	9,423,000	12,736,000	18,846,000
Expected net contributions						40,000,000	30,000,000
Capitalization of pension and OPEB expense related to engineering and plant construction		8,000,000	6,800,000
Estimated pension and other postretirement benefit expenses, minimum		75,000,000
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	25,500,000		438,800,000
Plan assets		1,271,600,000			1,258,000,000
Increase in plan assets		13,600,000
Percentage of increase in pension plan assets (in hundredths)		1.00%
Positive investment returns related to increase in plan assets		95,900,000
Benefit payments		$ 82,300,000