Retirement Plans and Postretirement Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Pension Plan Funding [Abstract]
Estimated future employer contributions	$ 35,000,000
Defined Benefit Plan, Fair Value of Plan Assets	589,800,000		574,000,000
Defined Benefit Plan, Expected Future Benefit Payments in Year One	68,200,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	69,200,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	87,000,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	78,300,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	71,100,000
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	303,300,000
Pension Plan Investments	618,900,000		588,200,000
Defined Benefit Plan, Effect of Plan Amendment on Accumulated Benefit Obligation	91,300,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	16,900,000
Reduction in Benefit Obligation Regulatory Asset Due to Plan Amendment	74,400,000
Postretirement Benefit Plans, Fair Value of Plan Assets	61,000,000		58,500,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	54,300,000		52,400,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Interest Income	1,300,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Unrealized Gains	900,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Dividends	800,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Realized Gains	100,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Administrative Expenses and Charges	(100,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Claims Paid	(1,100,000)
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	0		3,100,000		2,400,000
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	100,000		700,000		40,300,000
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	100,000		2,500,000		1,900,000
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	600,000		1,600,000		32,900,000
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	1,300,000
Postretirement Plan, Expected Future Benefit Payments in Year One	15,400,000
Postretirement Plan, Expected Future Benefit Payments in Year Two	16,000,000
Postretirement Plan, Expected Future Benefit Payments in Year Three	16,900,000
Postretirement Plan, Expected Future Benefit Payments in Year Four	17,700,000
Postretirement Plan, Expected Future Benefit Payments in Year Five	18,300,000
Postretirement Plan, Expected Future Benefit Payments Thereafter	97,000,000
Patient Protection and Affordable Care Act Eligible Claims Minimum	15,000
Patient Protection and Affordable Care Act Eligible Claims Maximum	90,000
Patient Protection and Affordable Care Act, Total Funding	5,000,000,000
Patient Protection and Affordable Care Act, Subsidy Received	700,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Increase in Postretirement Medical Expense	3,500,000
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	8.75%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.48%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	2028
Payments for Postemployment Benefits	2,400,000		2,100,000
Pension Contributions	50,000,000		50,000,000
Pension Plan [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Benefit Obligation	(697,700,000)		(640,900,000)		(610,900,000)
Defined Benefit Plan, Fair Value of Plan Assets	589,800,000		574,000,000		496,300,000
Defined Benefit Plan, Funded Status of Plan	(107,900,000)		(66,900,000)
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0		0
Defined Benefit Plan, Accumulated Benefit Obligation	656,100,000		601,400,000
Defined Benefit Plan, Plan Amendments	0		0
Contributions by employer	50,000,000		50,000,000
Defined Benefit Plan, Contributions by Plan Participants	0		0
Defined Benefit Plans, Medicare Subsidies Received	0		0
Defined Benefit Plan, Benefits Paid	(42,400,000)		(34,400,000)
Defined Benefit Plan, Actual Return on Plan Assets	8,200,000		62,100,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	(17,600,000)		(16,700,000)		(18,100,000)
Interest cost	(33,300,000)		(31,800,000)		(31,400,000)
Expected return on plan assets	45,500,000		42,400,000		33,000,000
Amortization of transition obligation	0		0		0
Amortization of net loss	19,200,000		21,300,000		23,500,000
Amortization of unrecognized prior service cost	2,400,000	[1]	2,400,000	[1]	800,000	[1]
Net Periodic Benefit Cost	27,000,000	[2]	29,800,000	[2]	40,800,000	[2]
Capitalized Portion of Net Periodic Benefit Cost	6,100,000		6,500,000		8,400,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net Periodic Benefit Cost	45,100,000		61,400,000		62,400,000
Postretirement Benefit Plans [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Benefit Obligation	(280,600,000)		(337,100,000)		(288,000,000)
Defined Benefit Plan, Fair Value of Plan Assets	61,000,000		58,500,000		55,000,000
Defined Benefit Plan, Funded Status of Plan	(219,600,000)		(278,600,000)
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	(2,000,000)		(1,400,000)
Defined Benefit Plan, Plan Amendments	91,400,000		0
Contributions by employer	6,600,000		7,100,000
Defined Benefit Plan, Contributions by Plan Participants	8,100,000		7,300,000
Defined Benefit Plans, Medicare Subsidies Received	2,000,000		1,400,000
Defined Benefit Plan, Benefits Paid	(16,900,000)		(17,500,000)
Defined Benefit Plan, Actual Return on Plan Assets	2,700,000		5,200,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	(3,500,000)		(4,300,000)		(3,300,000)
Interest cost	(12,500,000)		(17,000,000)		(14,100,000)
Expected return on plan assets	5,100,000		6,900,000		6,500,000
Amortization of transition obligation	2,700,000		2,700,000		2,700,000
Amortization of net loss	18,300,000		12,100,000		5,000,000
Amortization of unrecognized prior service cost	(16,500,000)	[1]	0	[1]	1,000,000	[1]
Net Periodic Benefit Cost	15,400,000	[2]	29,200,000	[2]	19,600,000	[2]
Capitalized Portion of Net Periodic Benefit Cost	3,800,000		6,500,000		4,100,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.50%		5.30%		6.00%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	6.50%		8.50%		8.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	8.75%		8.99%		9.49%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.48%		5.00%		5.00%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	2028		2020		2018
Restoration of Retirement Income Plan [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Benefit Obligation	(13,300,000)		(10,800,000)		(8,300,000)
Defined Benefit Plan, Fair Value of Plan Assets	0		0		0
Defined Benefit Plan, Funded Status of Plan	(13,300,000)		(10,800,000)
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0		0
Defined Benefit Plan, Accumulated Benefit Obligation	11,900,000		8,700,000
Defined Benefit Plan, Plan Amendments	0		0
Contributions by employer	100,000		400,000
Defined Benefit Plan, Contributions by Plan Participants	0		0
Defined Benefit Plans, Medicare Subsidies Received	0		0
Defined Benefit Plan, Benefits Paid	(100,000)		(400,000)
Defined Benefit Plan, Actual Return on Plan Assets	0		0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	(1,000,000)		(900,000)		(700,000)
Interest cost	(600,000)		(500,000)		(400,000)
Expected return on plan assets	0		0		0
Amortization of transition obligation	0		0		0
Amortization of net loss	400,000		300,000		300,000
Amortization of unrecognized prior service cost	700,000	[1]	700,000	[1]	600,000	[1]
Net Periodic Benefit Cost	2,700,000	[2]	2,400,000	[2]	2,000,000	[2]
401K [Member]
Pension Plan Funding [Abstract]
Contributions by employer	12,300,000		11,400,000		9,300,000
Less Than 90% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	50.00%
Projected Benefit Obligation Funded Status Thresholds Equity	50.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
95% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	58.00%
Projected Benefit Obligation Funded Status Thresholds Equity	42.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
100% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	65.00%
Projected Benefit Obligation Funded Status Thresholds Equity	35.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
105% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	73.00%
Projected Benefit Obligation Funded Status Thresholds Equity	27.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
110% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	80.00%
Projected Benefit Obligation Funded Status Thresholds Equity	20.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
115% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	85.00%
Projected Benefit Obligation Funded Status Thresholds Equity	15.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
120% [Member]
Pension Plan Funding [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income	90.00%
Projected Benefit Obligation Funded Status Thresholds Equity	10.00%
Projected Benefit Obligation Funded Status Thresholds	100.00%
Domestic All-Cap/Large Cap Equity [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	50.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Minimum	50.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Maximum	60.00%
Domestic Mid-Cap Equity [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	15.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Minimum	5.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Maximum	25.00%
Domestic Small-Cap Equity [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	15.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Minimum	5.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Maximum	25.00%
International Equity [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	20.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Minimum	10.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Range Maximum	30.00%
U.S. Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(179,700,000)		(189,000,000)
Foreign Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(59,500,000)		(75,900,000)
Corporate Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(95,300,000)	[3]	(104,100,000)	[3]
Collateralized Mortgage Backed Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(17,200,000)	[3]	(26,600,000)	[3]
US Treasury Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(118,800,000)	[4]	(35,700,000)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(72,000,000)		(76,500,000)
Other U.S. Government Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(1,000,000)		(2,400,000)
Equity Funds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(38,500,000)	[5]	(37,700,000)	[5]
Common Collective Trust [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(29,600,000)	[6]	(23,100,000)	[6]
Foreign Government Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(2,900,000)		(3,900,000)
Interest-bearing Deposits [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(2,100,000)		(200,000)
Municipal Bonds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(1,700,000)		(4,300,000)
Preferred Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(600,000)		(700,000)
Global Equity Mutual Fund [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,800,000)
Private Equity Funds, Domestic [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,600,000)
Private Equity Funds, Foreign [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,000,000)
Repurchase Agreements [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(3,700,000)
Receiveable From Broker For Securities Sold [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(4,800,000)		(5,500,000)
Interest and Dividends Receivable [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(3,100,000)		(2,800,000)
Payable to Broker for Securities Purchased [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	37,000,000		22,500,000
Fair Value, Inputs, Level 1 [Member]
Pension Plan Funding [Abstract]
Pension Plan Investments	360,700,000		305,900,000
Postretirement Benefit Plans, Fair Value of Plan Assets	6,700,000		6,100,000
Fair Value, Inputs, Level 1 [Member] | U.S. Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(179,700,000)		(189,000,000)
Fair Value, Inputs, Level 1 [Member] | Foreign Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(59,500,000)		(75,900,000)
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0	[3]	0	[3]
Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0	[3]	0	[3]
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(118,800,000)	[4]	(35,700,000)
Fair Value, Inputs, Level 1 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 1 [Member] | Other U.S. Government Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0	[5]	0	[5]
Fair Value, Inputs, Level 1 [Member] | Common Collective Trust [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0	[6]	0	[6]
Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 1 [Member] | Interest-bearing Deposits [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(2,100,000)		(200,000)
Fair Value, Inputs, Level 1 [Member] | Municipal Bonds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 1 [Member] | Preferred Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(600,000)		(700,000)
Fair Value, Inputs, Level 1 [Member] | Global Equity Mutual Fund [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,800,000)
Fair Value, Inputs, Level 1 [Member] | Private Equity Funds, Domestic [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,600,000)
Fair Value, Inputs, Level 1 [Member] | Private Equity Funds, Foreign [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(1,000,000)
Fair Value, Inputs, Level 1 [Member] | Repurchase Agreements [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			0
Fair Value, Inputs, Level 2 [Member]
Pension Plan Funding [Abstract]
Pension Plan Investments	258,200,000		282,300,000
Postretirement Benefit Plans, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 2 [Member] | U.S. Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 2 [Member] | Foreign Common Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(95,300,000)	[3]	(104,100,000)	[3]
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(17,200,000)	[3]	(26,600,000)	[3]
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0	[4]	0
Fair Value, Inputs, Level 2 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(72,000,000)		(76,500,000)
Fair Value, Inputs, Level 2 [Member] | Other U.S. Government Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(1,000,000)		(2,400,000)
Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(38,500,000)	[5]	(37,700,000)	[5]
Fair Value, Inputs, Level 2 [Member] | Common Collective Trust [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(29,600,000)	[6]	(23,100,000)	[6]
Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(2,900,000)		(3,900,000)
Fair Value, Inputs, Level 2 [Member] | Interest-bearing Deposits [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	(1,700,000)		(4,300,000)
Fair Value, Inputs, Level 2 [Member] | Preferred Stock [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Inputs, Level 2 [Member] | Global Equity Mutual Fund [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			0
Fair Value, Inputs, Level 2 [Member] | Private Equity Funds, Domestic [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			0
Fair Value, Inputs, Level 2 [Member] | Private Equity Funds, Foreign [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			0
Fair Value, Inputs, Level 2 [Member] | Repurchase Agreements [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets			(3,700,000)
Fair Value, Inputs, Level 3 [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Postretirement Benefit Plans, Fair Value of Plan Assets	54,300,000		52,400,000
Restoration of Retirement Income Plan [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.50%		5.30%		5.30%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.00%		8.50%		8.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	4.40%		4.40%		4.50%
Change in Benefit Obligation [Member] | Pension Plan [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Contributions by Plan Participants	0		0
Defined Benefit Plan, Actuarial Net (Gains) Losses	(48,300,000)		(15,900,000)
Defined Benefit Plan, Benefits Paid	42,400,000		34,400,000
Change in Benefit Obligation [Member] | Postretirement Benefit Plans [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Contributions by Plan Participants	(8,100,000)		(7,300,000)
Defined Benefit Plan, Actuarial Net (Gains) Losses	(25,700,000)		(36,600,000)
Defined Benefit Plan, Benefits Paid	16,900,000		17,500,000
Change in Benefit Obligation [Member] | Restoration of Retirement Income Plan [Member]
Pension Plan Funding [Abstract]
Defined Benefit Plan, Contributions by Plan Participants	0		0
Defined Benefit Plan, Actuarial Net (Gains) Losses	(1,000,000)		(1,500,000)
Defined Benefit Plan, Benefits Paid	100,000		400,000
Group Retiree Medical Insurance Contract [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	54,300,000	[7]	52,400,000	[7]
Group Retiree Medical Insurance Contract [Member] | Fair Value, Inputs, Level 1 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	0	[7]	0	[7]
Group Retiree Medical Insurance Contract [Member] | Fair Value, Inputs, Level 3 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	54,300,000	[7]	52,400,000	[7]
U.S. Equity Mutual Funds Investment [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	5,300,000		5,500,000
U.S. Equity Mutual Funds Investment [Member] | Fair Value, Inputs, Level 1 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	5,300,000		5,500,000
U.S. Equity Mutual Funds Investment [Member] | Fair Value, Inputs, Level 3 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	0		0
Money Market Funds [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	700,000		600,000
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	700,000		600,000
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	0		0
Cash [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	700,000
Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	700,000
Cash [Member] | Fair Value, Inputs, Level 3 [Member]
Pension Plan Funding [Abstract]
Postretirement Benefit Plans, Fair Value of Plan Assets	0
OKLAHOMA | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements	10,800,000		8,100,000		2,200,000
ARKANSAS | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements					$ 3,200,000

[1] (A) Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.

[2] (B) In addition to the $45.1 million, $61.4 million and $62.4 million of net periodic benefit cost recognized in 2011, 2010 and 2009, respectively, the Company recognized the following: •an increase in pension expense in 2011 and 2010 of $10.8 million and $8.1 million, respectively, and a reduction in pension expense in 2009 of $2.2 million to maintain the allowable amount to be recovered for pension expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory liability (see Note 1); •a reduction in pension expense in 2009 of $3.2 million in the Arkansas jurisdiction to reflect the approval of recovery of OG&E's 2006 and 2007 pension settlement costs in the May 2009 Arkansas rate order which are included in the Pension tracker regulatory liability) (see Note 1); and •an increase in postretirement medical expense in 2011 of $3.5 million to maintain the allowable amount to be recovered for postretirement medical expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory liability (see Note 1).

[3] (A) This category primarily represents U.S. corporate bonds with an investment grade rating at or above Baa3 or BBB- by Moody's Investors Services, Standard & Poor's Ratings Services or Fitch Ratings.

[4] (B) This category represents U.S. treasury notes and bonds with a Moody's Investors Services rating of Aaa and Government Agency Bonds with a Moody's Investors Services rating of A1 or higher.

[5] (C) This category represents units of participation in a commingled fund that primarily invest in stocks and bonds of U.S. companies.

[6] (D) This category represents units of participation in an investment pool which primarily invests in foreign or domestic bonds, debentures, mortgages, equipment or other trust certificates, notes, obligations issued or guaranteed by the U.S. Government or its agencies, bank certificates of deposit, bankers' acceptances and repurchase agreements, high grade commercial paper and other instruments with money market characteristics with a fixed or variable interest rate. There are no restrictions on redemptions in the common/collective trust.

[7] (A) This category represents a group retiree medical insurance contract which invests in a pool of common stocks, bonds and money market accounts, of which a significant portion is comprised of mortgage-backed securities.