Retirement Plans and Postretirement Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost (net of unconsolidated affiliates)	$ 2.4		$ 6.6
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	4.3		5.0
Interest cost	7.0		6.6
Expected return on plan assets	(12.5)		(12.3)
Amortization of net loss	3.5		6.2
Amortization of unrecognized prior service cost	0.4	[1]	0.5	[1]
Total net periodic benefit cost	2.7		6.0
Less: Amount paid by unconsolidated affiliates	0.8		0
Net periodic benefit cost (net of unconsolidated affiliates)	1.9	[2]	6.0	[2]
Capitalized Portion of Net Periodic Benefit Cost	0.6		1.6
Restoration of Retirement Income Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.3		0.3
Interest cost	0.2		0.1
Expected return on plan assets	0		0
Amortization of net loss	0		0.1
Amortization of unrecognized prior service cost	0	[1]	0.1	[1]
Total net periodic benefit cost	0.5		0.6
Less: Amount paid by unconsolidated affiliates	0		0
Net periodic benefit cost (net of unconsolidated affiliates)	0.5	[2]	0.6	[2]
Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.9		1.2
Interest cost	2.8		2.6
Expected return on plan assets	(0.6)		(0.6)
Amortization of net loss	3.1		5.3
Amortization of unrecognized prior service cost	(4.1)	[1]	(4.1)	[1]
Total net periodic benefit cost	2.1		4.4
Less: Amount paid by unconsolidated affiliates	0.3		0
Net periodic benefit cost (net of unconsolidated affiliates)	1.8	[3]	4.4	[3]
Capitalized Portion of Net Periodic Benefit Cost	0.5		1.3
OKLAHOMA | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements	3.3		1.9
OKLAHOMA | Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements	$ 1.2		$ 0.1

[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 $2.4 million and $6.6 million of net periodic benefit cost recognized during the three months ended March 31, 2014 and 2013, respectively, OG&E recognized an increase in pension expense during the three months ended March 31, 2014 and 2013 of $3.3 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 $1.8 million and $4.4 million of net periodic benefit cost recognized during the three months ended March 31, 2014 and 2013, respectively, OG&E recognized an increase in postretirement medical expense during the three months ended March 31, 2014 and 2013 of $1.2 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).