Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost (net of unconsolidated affiliates)		$ 3.3		$ 3.8		$ 6.4		$ 6.2
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		3.4		3.3		7.9		7.6
Interest cost		6.6		7.1		13.0		14.1
Expected return on plan assets		(11.7)		(10.2)		(23.5)		(22.7)
Amortization of net loss		5.4		3.6		9.7		7.1
Amortization of unrecognized prior service cost	[1]	0.1		0.5		0.2		0.9
Total net periodic benefit cost		3.8		4.3		7.3		7.0
Less: Amount paid by unconsolidated affiliates		1.0		0.9		2.1		1.7
Net periodic benefit cost (net of unconsolidated affiliates)		2.8	[2]	3.4	[2]	5.2	[3]	5.3	[3]
Capitalized Portion of Net Periodic Benefit Cost		1.2		1.1		2.0		1.7
Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		0.2	[2]	0.2	[2]	0.6		0.5
Interest cost		0.1	[2]	0.1	[2]	0.3		0.3
Expected return on plan assets		0.0	[2]	0.0	[2]	0.0		0.0
Amortization of net loss		0.2	[2]	0.1	[2]	0.3		0.1
Amortization of unrecognized prior service cost	[1]	0.1	[2]	0.1	[2]	0.1		0.1
Total net periodic benefit cost		0.6		0.5		1.3		1.0
Less: Amount paid by unconsolidated affiliates		0.1		0.1		0.1		0.1
Net periodic benefit cost (net of unconsolidated affiliates)		0.5	[2]	0.4	[2]	1.2	[3]	0.9	[3]
Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		0.3		0.7		0.8		1.6
Interest cost		2.5		2.9		5.1		5.7
Expected return on plan assets		(0.6)		(0.6)		(1.2)		(1.2)
Amortization of net loss		3.5		3.1		6.9		6.2
Amortization of unrecognized prior service cost	[1]	(4.2)		(4.2)		(8.3)		(8.3)
Total net periodic benefit cost		1.5		1.9		3.3		4.0
Less: Amount paid by unconsolidated affiliates		0.3		0.4		0.6		0.7
Net periodic benefit cost (net of unconsolidated affiliates)		1.2	[4]	1.5	[4]	2.7	[5]	3.3	[5]
Capitalized Portion of Net Periodic Benefit Cost		0.4		0.5		0.9		1.0
OKLAHOMA
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements		2.4		2.3		5.4		5.6
OKLAHOMA | Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Additional Pension Expense to Meet State Requirements		$ 1.5		$ 1.4		$ 2.9		$ 2.6

[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 $3.3 million and $3.8 million of net periodic benefit cost recognized during the three months ended June 30, 2015 and 2014, respectively, OG&E recognized an increase in pension expense during the three months ended June 30, 2015 and 2014 of $2.4 million and $2.3 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 $6.4 million and $6.2 million of net periodic benefit cost recognized during the six months ended June 30, 2015 and 2014, respectively, OG&E recognized an increase in pension expense during the six months ended June 30, 2015 and 2014 of $5.4 million and $5.6 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 $1.2 million and $1.5 million of net periodic benefit cost recognized during the three months ended June 30, 2015 and 2014, respectively, OG&E recognized an increase in postretirement medical expense during the three months ended June 30, 2015 and 2014 of $1.5 million and $1.4 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 $2.7 million and $3.3 million of net periodic benefit cost recognized during the six months ended June 30, 2015 and 2014, respectively, OG&E recognized an increase in postretirement medical expense during the six months ended June 30, 2015 and 2014 of $2.9 million and $2.6 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).