Retirement Plans and Postretirement Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$ 35
Defined Benefit Plan, Contributions by Employer	35
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost (net of unconsolidated affiliates)	5.4		7.7		18.4		23.0
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	4.8		4.5		14.3		13.5
Interest cost	6.6		7.5		20.0		22.5
Expected return on plan assets	(12.1)		(11.5)		(36.3)		(34.5)
Amortization of net loss	6.6		6.0		19.8		17.9
Amortization of unrecognized prior service cost	0.5	[1]	0.5	[1]	1.4	[1]	1.6	[1]
Total net periodic benefit cost	6.4		7.0		19.2		21.0
Less: Amount paid by unconsolidated affiliates	1.5		0		2.5		0
Net periodic benefit cost (net of unconsolidated affiliates)	4.9	[2]	7.0	[2]	16.7	[3]	21.0	[3]
Capitalized Portion of Net Periodic Benefit Cost	1.1		1.6		3.7		4.7
Restoration of Retirement Income Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.3		0.3		0.9		0.8
Interest cost	0.1		0.1		0.4		0.4
Expected return on plan assets	0		0		0		0
Amortization of net loss	0.1		0.1		0.3		0.3
Amortization of unrecognized prior service cost	0.1	[1]	0.2	[1]	0.2	[1]	0.5	[1]
Total net periodic benefit cost	0.6		0.7		1.8		2.0
Less: Amount paid by unconsolidated affiliates	0.1		0		0.1		0
Net periodic benefit cost (net of unconsolidated affiliates)	0.5	[2]	0.7	[2]	1.7	[3]	2.0	[3]
Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	1.1		1.0		3.3		3.1
Interest cost	2.5		2.9		7.7		8.9
Expected return on plan assets	(0.6)		(0.8)		(1.9)		(2.3)
Amortization of transition obligation	0		0.7		0		2.1
Amortization of net loss	5.4		5.2		16.1		15.4
Amortization of unrecognized prior service cost	(4.1)	[1]	(4.1)	[1]	(12.4)	[1]	(12.4)	[1]
Total net periodic benefit cost	4.3		4.9		12.8		14.8
Less: Amount paid by unconsolidated affiliates	0.6		0		1.0		0
Net periodic benefit cost (net of unconsolidated affiliates)	3.7	[4]	4.9	[4]	11.8	[5]	14.8	[5]
Capitalized Portion of Net Periodic Benefit Cost	0.7		1.0		2.3		3.0
OKLAHOMA | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements	1.5		1.9		4.6		7.6
OKLAHOMA | Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements	$ 0.1		$ 0.1		$ 0.4		$ 0.8

[1] 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] In addition to the $5.4 million and $7.7 million of net periodic benefit cost recognized during the three months ended September 30, 2013 and 2012, respectively, OG&E recognized an increase in pension expense during the three months ended September 30, 2013 and 2012 of $1.5 million and $1.9 million, respectively, 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).

[3] In addition to the $18.4 million and $23.0 million of net periodic benefit cost recognized during the nine months ended September 30, 2013 and 2012, respectively, OG&E recognized an increase in pension expense during the nine months ended September 30, 2013 and 2012 of $4.6 million and $7.6 million, respectively, 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).

[4] In addition to the $3.7 million and $4.9 million of net periodic benefit cost recognized during the three months ended September 30, 2013 and 2012, respectively, OG&E recognized an increase in postretirement medical expense during the three months ended September 30, 2013 and 2012 of $0.1 million and $0.1 million, respectively, 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).

[5] In addition to the $11.8 million and $14.8 million of net periodic benefit cost recognized during the nine months ended September 30, 2013 and 2012, respectively, OG&E recognized an increase in postretirement medical expense during the nine months ended September 30, 2013 and 2012 of $0.4 million and $0.8 million, respectively, 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).