Retirement Plans (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Description of published surveys of expected market returns considered			Published surveys of expected market returns, 10 and 20 year actual returns of various major indices
Description of historical investment returns considered			Our own historical 5-year, 10-year and 20-year investment returns
Annual rate of increase in the per-capita cost of covered medical benefits, lower range (in hundredths)			5.00%
Annual rate of increase in the per-capita cost of covered medical benefits, upper range (in hundredths)			8.00%
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits	$ (1,055,058,000)		$ (1,055,058,000)		$ (918,701,000)
Components of net periodic benefit cost [Abstract]
Cash contribution to the Plan	10,300,000	18,300,000			18,600,000		13,100,000
Expected cash contributions in 2013	60,000,000		60,000,000
Accumulated benefit obligation	1,793,800,000		1,793,800,000		1,673,400,000
Number of pension plans that were merged with the pension plan	12		12
401 (k) Savings Plan employer contributions			23,000,000		22,200,000		14,900,000
401 (k) Savings Plan employer contributions for certain former employees of the Acquired Business					15,900,000		10,600,000
Number of separate plans of the Acquired Business	3		3
Assumed rate of return (in hundredths)			8.00%
Capitalization of pension and OPEB expense related to engineering and plant construction			15,800,000		10,200,000		8,300,000
Range of full year estimated pension and other postretirement benefit expenses lower			100,000,000
Range of full year estimated pension and other postretirement benefit expenses upper			110,000,000
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	113,424,000		113,424,000
2014	120,836,000		120,836,000
2015	128,624,000		128,624,000
2016	134,922,000		134,922,000
2017	138,759,000		138,759,000
2018 - 2022	729,847,000		729,847,000
Total	1,366,412,000		1,366,412,000
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Annual rate of increase in the per-capita cost of covered medical benefits (in hundredths)			8.00%
Annual rate of increase in the per-capita cost of covered medical benefits in 2019 (in hundredths)			5.00%
Effect on total of service and interest cost components, 1 percentage point increase			1,300,000
Effect on postretirement benefit obligation, 1 percentage point increase			19,800,000
Effect on total of service and interest cost components, 1 percentage point decrease			(1,000,000)
Effect on postretirement benefit obligation, 1 percentage point decrease			(16,100,000)
Percentage of federal subsidy (in hundredths)			28.00%
Individual beneficiary's annual eligible prescription drug costs, lower range	250		250
Individual beneficiary's annual eligible prescription drug costs, upper range	5,000		5,000
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Expected long-term rate of return on plan assets (in hundredths)			8.00%
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Total contributions to Pension Plan			28,600,000		76,700,000
Pension Plan [Member]
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year			1,799,313,000		1,644,657,000
Service cost			43,688,000		38,879,000		21,169,000
Interest cost			78,027,000		84,228,000		67,735,000
Actuarial loss			196,304,000		160,390,000
Benefits paid			(172,601,000)		(128,841,000)
PBO at end of year	1,944,731,000		1,944,731,000		1,799,313,000		1,644,657,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year			1,257,990,000		1,290,274,000
Actual return on plan assets			139,679,000		19,883,000
Employer contributions			28,598,000		76,674,000
Benefits paid			(172,601,000)		(128,841,000)
Fair value of plan assets at end of year	1,253,666,000		1,253,666,000		1,257,990,000		1,290,274,000
Funded status	(691,065,000)		(691,065,000)		(541,323,000)
Amounts recognized in the consolidated balance sheet [Abstract]
Current liabilities	(60,386,000)		(60,386,000)		0
Pension and other postretirement benefits	(630,679,000)		(630,679,000)		(541,323,000)
Accumulated other comprehensive loss	697,874,000		697,874,000		575,163,000
Components of net periodic benefit cost [Abstract]
Service cost			43,688,000		38,879,000		21,169,000
Interest cost on projected benefit obligation			78,027,000		84,228,000		67,735,000
Expected return on plan assets			(95,777,000)		(100,558,000)		(69,831,000)
Amortization of prior service cost/credit			(199,000)	[1],[2]	(199,000)	[1],[2]	(199,000)	[1],[2]
Amortization of prior service cost/(credit) expected in 2013	(8,000)		(8,000)
Amortization of unrecognized loss			29,890,000	[1],[2]	15,364,000	[1],[2]	27,393,000	[1],[2]
Amortization of unrecognized loss expected in 2013	40,287,000		40,287,000
Net periodic postretirement benefit cost			55,629,000		37,714,000		46,267,000
Special termination charge			0		0		69,000
Total periodic benefit cost			55,629,000		37,714,000		46,336,000
Assumed rate of return (in hundredths)			7.75%		8.00%		8.00%
Asset category [Abstract]
Alternative investments (in hundredths)	14.00%		14.00%		14.00%
Cash and other (in hundredths)	3.00%		3.00%		1.00%
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	4.00%		4.00%		4.50%		5.25%
Discount rate - used to compute annual cost (in hundredths)			4.50%		5.25%		5.75%
Expected long-term rate of return on plan assets (in hundredths)			7.75%		8.00%		8.00%
Rate of increase in compensation levels (in hundredths)			2.50%		2.50%		3.00%
Defined Benefit Plan
Net actuarial loss	697,511,000		697,511,000		574,998,000
Prior service cost/(credit)	363,000		363,000		165,000
Total	697,874,000		697,874,000		575,163,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Accumulated other comprehensive income at beginning of year			575,163,000		349,264,000
Net actuarial gain (loss) recognized during year			(29,890,000)		(15,364,000)
Prior service (cost)/credit recognized during year			199,000		199,000
Net actuarial loss (gain) occurring during year			152,402,000		241,064,000
Prior service cost (credit) occurring during year			0		0
Net amount recognized in comprehensive income for the year			122,711,000		225,899,000
Accumulated other comprehensive income at end of year	697,874,000		697,874,000		575,163,000		349,264,000
OPEB [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on plan assets, upper range (in hundredths)	4.00%		4.00%		6.00%
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year			391,596,000		353,131,000
Service cost			10,812,000		8,958,000		7,956,000
Interest cost			17,842,000		17,722,000		17,883,000
Plan participants' contributions			4,059,000		4,389,000
Actuarial loss			30,958,000		22,564,000
Benefits paid			(15,974,000)		(15,168,000)
Plan change			(743,000)		0
PBO at end of year	438,550,000		438,550,000		391,596,000		353,131,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year			5,101,000		6,240,000
Actual return on plan assets			466,000		219,000
Plan participant's contributions			4,059,000		4,389,000
Employer contributions			11,403,000		9,421,000
Benefits paid			(15,974,000)		(15,168,000)
Fair value of plan assets at end of year	5,055,000		5,055,000		5,101,000		6,240,000
Funded status	(433,495,000)		(433,495,000)		(386,495,000)
Amounts recognized in the consolidated balance sheet [Abstract]
Current liabilities	(9,116,000)		(9,116,000)		(9,117,000)
Pension and other postretirement benefits	(424,379,000)		(424,379,000)		(377,378,000)
Accumulated other comprehensive loss	74,264,000		74,264,000		41,811,000
Components of net periodic benefit cost [Abstract]
Service cost			10,812,000		8,958,000		7,956,000
Interest cost on projected benefit obligation			17,842,000		17,722,000		17,883,000
Expected return on plan assets			(172,000)		(324,000)		(436,000)
Amortization of prior service cost/credit			(10,068,000)		(10,198,000)		(8,157,000)
Amortization of prior service cost/(credit) expected in 2013	(6,101,000)		(6,101,000)
Amortization of unrecognized loss			7,537,000		4,424,000		4,917,000
Amortization of unrecognized loss expected in 2013	8,911,000		8,911,000
Net periodic postretirement benefit cost			25,951,000		20,582,000		22,163,000
Assumed rate of return (in hundredths)							6.00%
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	13,580,000		13,580,000
2014	15,058,000		15,058,000
2015	16,804,000		16,804,000
2016	18,697,000		18,697,000
2017	20,423,000		20,423,000
2018 - 2022	123,572,000		123,572,000
Total	208,134,000		208,134,000
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation, lower range (in hundredths)	4.00%		4.00%		4.50%
Discount rate - used at year end to value obligation, upper range (in hundredths)	4.20%		4.20%		4.75%
Discount rate - used at year end to value obligation (in hundredths)							5.25%
Discount rate - used to compute annual cost, lower range (in hundredths)			4.50%
Discount rate - used to compute annual cost, upper range (in hundredths)			4.75%
Discount rate - used to compute annual cost (in hundredths)					5.25%		5.75%
Expected long term rate of return on plan assets, lower range (in hundredths)	3.00%		3.00%		3.00%
Expected long term rate of return on plan assets, upper range (in hundredths)	4.00%		4.00%		6.00%
Expected long-term rate of return on plan assets (in hundredths)							6.00%
Defined Benefit Plan
Net actuarial loss	105,970,000		105,970,000		82,841,000
Prior service cost/(credit)	(31,706,000)		(31,706,000)		(41,030,000)
Total	74,264,000		74,264,000		41,811,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Accumulated other comprehensive income at beginning of year			41,811,000		13,369,000
Net actuarial gain (loss) recognized during year			(7,537,000)		(4,424,000)
Prior service (cost)/credit recognized during year			10,068,000		10,198,000
Net actuarial loss (gain) occurring during year			30,665,000		22,668,000
Prior service cost (credit) occurring during year			(743,000)		0
Net amount recognized in comprehensive income for the year			32,453,000		28,442,000
Accumulated other comprehensive income at end of year	74,264,000		74,264,000		41,811,000		13,369,000
OPEB, Gross Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	14,010,000		14,010,000
2014	15,591,000		15,591,000
2015	17,448,000		17,448,000
2016	19,457,000		19,457,000
2017	21,347,000		21,347,000
2018 - 2022	131,410,000		131,410,000
Total	219,263,000		219,263,000
Medicare Part D Subsidy [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	430,000		430,000
2014	533,000		533,000
2015	644,000		644,000
2016	760,000		760,000
2017	924,000		924,000
2018 - 2022	7,838,000		7,838,000
Total	11,129,000		11,129,000
Pension Plan Noncash Contribution [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of year					$ 58,100,000
Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on plan assets, upper range (in hundredths)	55.00%		55.00%
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Expected long term rate of return on plan assets, lower range (in hundredths)	35.00%		35.00%
Expected long term rate of return on plan assets, upper range (in hundredths)	55.00%		55.00%
Equity Securities [Member] | Pension Plan [Member]
Asset category [Abstract]
Investment securities (in hundredths)	43.00%		43.00%		45.00%
Debt Securities [Member] | Pension Plan [Member]
Asset category [Abstract]
Investment securities (in hundredths)	40.00%		40.00%		40.00%
Fixed Income [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on plan assets, upper range (in hundredths)	55.00%		55.00%
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Expected long term rate of return on plan assets, lower range (in hundredths)	35.00%		35.00%
Expected long term rate of return on plan assets, upper range (in hundredths)	55.00%		55.00%
Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on plan assets, upper range (in hundredths)	15.00%		15.00%
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Expected long term rate of return on plan assets, lower range (in hundredths)	5.00%		5.00%
Expected long term rate of return on plan assets, upper range (in hundredths)	15.00%		15.00%

[1] These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 17 - Retirement Plans for additional details).

[2] Amounts in parentheses indicate debits.