Financing Activities (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
		Jul. 26, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Long-term Debt
Senior Unsecured Notes			$ 17,461.1		$ 17,461.1		$ 16,478.3
Pollution Control Bonds			1,643.4		1,643.4		1,621.7
Notes Payable			263.2		263.2		260.8
Securitization Bonds			1,258.7		1,258.7		1,416.5
Spent Nuclear Fuel Obligation	[1]		270.8		270.8		268.6
Other Long-term Debt			1,134.8		1,134.8		1,127.4
Total Long-term Debt Outstanding			22,032.0		22,032.0		21,173.3
Long-term Debt Due Within One Year			2,281.4		2,281.4		1,753.7
Long-term Debt			19,750.6		19,750.6		19,419.6
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				2,233.6
Retirements and Principal Payments					1,339.8	$ 1,899.3
Short-term Debt:
Securitized Debt for Receivables	[3]		750.0		750.0		718.0
Commercial Paper			1,814.0		1,814.0		898.6
Notes Payable			25.2		25.2		22.0
Total Short-term Debt			$ 2,589.2		$ 2,589.2		$ 1,638.6
Securitized Debt for Receivables	[3],[4]		1.95%		1.95%		1.22%
Comparative Accounts Receivable Information
Effective Interest Rates on Securitization of Accounts Receivable			2.16%	1.17%	1.95%	1.09%
Net Uncollectible Accounts Receivable Written Off			$ 5.3	$ 5.3	$ 9.4	$ 11.2
Customer Accounts Receivable Managed Portfolio
Accounts Receivable Retained Interest and Pledged as Collateral Less Uncollectible Accounts			1,101.4		1,101.4		$ 925.5
Total Principal Outstanding			750.0		750.0		718.0
Delinquent Securitized Accounts Receivable			55.2		55.2		41.1
Bad Debt Reserves Related to Securitization, Sale of Accounts Receivable			32.0		32.0		28.7
Unbilled Receivables Related to Securitization, Sale of Accounts Receivable			332.8		332.8		303.2
Financing Activities (Textuals) [Abstract]
Trust Fund Assets One Time Fee Obligation for Nuclear Fuel Disposition			314.0		314.0		$ 312.0
Repayments of Long-term Debt					1,339.8	1,899.3
Reacquired Pollution Controls Bonds Held by Trustees			574.0		$ 574.0
Maximum Percentage Debt to Capitalization					67.50%
Total Commitment from Bank Conduits to Finance Receivables			$ 750.0		$ 750.0
Commercial Paper [Member]
Short-term Debt:
Weighted Average Interest Rate	[4]		2.41%		2.41%		1.85%
Loans Payable [Member]
Short-term Debt:
Weighted Average Interest Rate	[4]		3.35%		3.35%		2.92%
AEP Subsidiaries [Member]
Long-term Debt
Long-term Debt Due Within One Year			$ 423.2		$ 423.2		$ 406.9
Long-term Debt			1,247.3		1,247.3		1,410.5
AEP Texas Inc. [Member]
Long-term Debt
Total Long-term Debt Outstanding			3,991.3		3,991.3		3,649.3
Long-term Debt Due Within One Year			293.7		293.7		266.1
Long-term Debt			3,697.6		3,697.6		3,383.2
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					154.1	117.1
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 154.1	$ 117.1
Maximum Percentage Debt to Capitalization					67.50%
AEP Texas Inc. [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 390.6
Maximum Loans to Money Pool					106.9
Average Borrowings from Money Pool					265.6
Average Loans to Money Pool					60.5
Net Loans (Borrowings) to/from Money Pool			19.0		19.0
Authorized Short Term Borrowing Limit					$ 500.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.28%	1.18%
Average Interest Rate For Funds Loaned					2.28%	0.00%
AEP Texas Inc. [Member] | Nonutility [Member]
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Loans to Money Pool					$ 8.4
Average Loans to Money Pool					8.1
Net Loans (Borrowings) to/from Money Pool			$ 8.1		$ 8.1
Maximum and Minimum Interest Rates
Maximum Interest Rate For Funds Loaned					2.52%	1.44%
Minimum Interest Rate for Funds Loaned					1.83%	0.00%
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Loaned					2.23%	1.17%
AEP Texas Inc. [Member] | Securitization Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 70.0
Interest Rate (Percentage)			5.17%		5.17%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 70.0
AEP Texas Inc. [Member] | Securitization Bonds [Member] | Subsequent Event [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments		$ 78.0
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt		78.0
AEP Texas Inc. [Member] | Securitization Bonds Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 27.6
Interest Rate (Percentage)			1.976%		1.976%
Due Date					2020
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 27.6
AEP Texas Inc. [Member] | Securitization Bonds Three [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 26.5
Interest Rate (Percentage)			5.306%		5.306%
Due Date					2020
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 26.5
AEP Texas Inc. [Member] | Senior Unsecured Notes [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 500.0
Interest Rate (Percentage)			3.95%		3.95%
Due Date					2028
AEP Texas Inc. [Member] | Senior Unsecured Notes Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 30.0
Interest Rate (Percentage)			5.89%		5.89%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 30.0
AEP Transmission Co [Member]
Long-term Debt
Total Long-term Debt Outstanding			$ 2,550.9		2,550.9		2,550.4
Long-term Debt Due Within One Year			50.0		50.0		50.0
Long-term Debt			2,500.9		2,500.9		2,500.4
Financing Activities (Textuals) [Abstract]
Sub-Limit of Secured Debt			$ 50.0		$ 50.0
Maximum Percentage of Consolidated Tangible Net Assets			10.00%		10.00%
Tangible Capital to Tangible Assets			2.50%		2.50%
Maximum Percentage Debt to Capitalization					67.50%
AEP Transmission Co [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 371.3
Maximum Loans to Money Pool					123.9
Average Borrowings from Money Pool					235.5
Average Loans to Money Pool					17.6
Net Loans (Borrowings) to/from Money Pool			$ (142.8)		(142.8)
Authorized Short Term Borrowing Limit	[5]				$ 795.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.30%	1.25%
Average Interest Rate For Funds Loaned					2.06%	0.99%
AEP Transmission Co [Member] | Direct Borrowing [Member]
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 1.1
Maximum Loans to Money Pool					104.7
Average Borrowings from Money Pool					1.1
Average Loans to Money Pool					48.4
Borrowings from Parent			1.1		1.1
Loans to Parent			30.0		30.0
Authorized Short Term Borrowing Limit	[6]				$ 75.0
Maximum and Minimum Interest Rates
Maximum Interest Rate for Funds Borrowed					2.52%	1.44%
Minimum Interest Rate For Funds Borrowed					1.83%	0.92%
Maximum Interest Rate For Funds Loaned					2.52%	1.44%
Minimum Interest Rate for Funds Loaned					1.83%	0.92%
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.23%	1.18%
Average Interest Rate For Funds Loaned					2.23%	1.21%
Appalachian Power Co [Member]
Long-term Debt
Total Long-term Debt Outstanding			4,073.7		$ 4,073.7		3,980.1
Long-term Debt Due Within One Year			530.5		530.5		249.2
Long-term Debt			3,543.2		3,543.2		3,730.9
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					11.7	$ 365.9
Accounts Receivable and Accrued Unbilled Revenues
Accounts Receivable and Accrued Unbilled Revenues			138.6		138.6		136.2
Fees Paid to AEP Credit for Customer Accounts Receivable Sold
Fees Paid to AEP Credit for Customer Accounts Receivable Sold			1.6	1.3	3.3	2.7
Proceeds from Sale of Receivables
Proceeds from Sale of Receivables to AEP Credit			344.9	324.2	745.1	693.9
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 11.7	$ 365.9
Maximum Percentage Debt to Capitalization					67.50%
Appalachian Power Co [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 295.5
Maximum Loans to Money Pool					23.7
Average Borrowings from Money Pool					224.3
Average Loans to Money Pool					23.5
Net Loans (Borrowings) to/from Money Pool			$ (149.3)		(149.3)
Authorized Short Term Borrowing Limit					$ 600.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.23%	1.17%
Average Interest Rate For Funds Loaned					2.23%	1.22%
Appalachian Power Co [Member] | Pollution Control Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 104.4
Interest Rate (Percentage)			2.625%		2.625%
Due Date					2022
Appalachian Power Co [Member] | Securitization Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 11.7
Interest Rate (Percentage)			2.008%		2.008%
Due Date					2023
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 11.7
Indiana Michigan Power Co [Member]
Long-term Debt
Total Long-term Debt Outstanding			$ 3,096.8		3,096.8		2,745.1
Long-term Debt Due Within One Year			657.6		657.6		474.7
Long-term Debt			2,439.2		2,439.2		2,270.4
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					352.4	$ 193.3
Accounts Receivable and Accrued Unbilled Revenues
Accounts Receivable and Accrued Unbilled Revenues			166.3		166.3		136.5
Fees Paid to AEP Credit for Customer Accounts Receivable Sold
Fees Paid to AEP Credit for Customer Accounts Receivable Sold			2.2	1.6	4.3	3.1
Proceeds from Sale of Receivables
Proceeds from Sale of Receivables to AEP Credit			444.2	390.7	903.3	809.0
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 352.4	$ 193.3
Maximum Percentage Debt to Capitalization					67.50%
Indiana Michigan Power Co [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 322.1
Maximum Loans to Money Pool					124.2
Average Borrowings from Money Pool					257.6
Average Loans to Money Pool					34.3
Net Loans (Borrowings) to/from Money Pool			$ 92.3		92.3
Authorized Short Term Borrowing Limit					$ 500.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.16%	1.20%
Average Interest Rate For Funds Loaned					2.37%	1.18%
Indiana Michigan Power Co [Member] | Notes Payable, Other Payables [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 55.5
Interest Rate (Variable)					Variable
Due Date					2022
Indiana Michigan Power Co [Member] | Notes Payable, Other Payables [Member] | Subsequent Event [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments		4.0
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt		4.0
Indiana Michigan Power Co [Member] | Notes Payable, Other Payable Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 2.1
Interest Rate (Variable)					Variable
Due Date					2019
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 2.1
Indiana Michigan Power Co [Member] | Notes Payable, Other Payable Three [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 8.7
Interest Rate (Variable)					Variable
Due Date					2019
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 8.7
Indiana Michigan Power Co [Member] | Notes Payable, Other Payable Four [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 11.8
Interest Rate (Variable)					Variable
Due Date					2020
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 11.8
Indiana Michigan Power Co [Member] | Notes Payable, Other Payable Five [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 13.5
Interest Rate (Variable)					Variable
Due Date					2021
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 13.5
Indiana Michigan Power Co [Member] | Notes Payable, Other Payables Six [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 14.2
Interest Rate (Variable)					Variable
Due Date					2022
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 14.2
Indiana Michigan Power Co [Member] | Notes Payable, Other Payable Seven [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 1.3
Interest Rate (Variable)					Variable
Due Date					2022
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 1.3
Indiana Michigan Power Co [Member] | Other Long Term Debt [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 200.0
Interest Rate (Variable)					Variable
Due Date					2021
Indiana Michigan Power Co [Member] | Other Long Term Debt Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 200.0
Interest Rate (Variable)					Variable
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 200.0
Indiana Michigan Power Co [Member] | Other Long Term Debt Three [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 0.8
Interest Rate (Percentage)			6.00%		6.00%
Due Date					2025
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 0.8
Indiana Michigan Power Co [Member] | Pollution Control Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 100.0
Interest Rate (Percentage)			3.05%		3.05%
Due Date					2025
Indiana Michigan Power Co [Member] | Pollution Control Bonds Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 100.0
Interest Rate (Percentage)			1.75%		1.75%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 100.0
Indiana Michigan Power Co [Member] | Senior Unsecured Notes [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 350.0
Interest Rate (Percentage)			3.85%		3.85%
Due Date					2028
Ohio Power Co [Member]
Long-term Debt
Total Long-term Debt Outstanding			$ 1,740.0		$ 1,740.0		1,719.3
Long-term Debt Due Within One Year			47.5		47.5		397.0
Long-term Debt			1,692.5		1,692.5		1,322.3
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					372.9	$ 22.5
Accounts Receivable and Accrued Unbilled Revenues
Accounts Receivable and Accrued Unbilled Revenues			420.4		420.4		367.4
Fees Paid to AEP Credit for Customer Accounts Receivable Sold
Fees Paid to AEP Credit for Customer Accounts Receivable Sold			6.0	4.7	11.6	10.4
Proceeds from Sale of Receivables
Proceeds from Sale of Receivables to AEP Credit			671.7	493.1	1,351.7	1,125.4
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					372.9	$ 22.5
Reacquired Pollution Controls Bonds Held by Trustees			345.0		$ 345.0
Ohio Power Co [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 234.0
Maximum Loans to Money Pool					225.0
Average Borrowings from Money Pool					135.7
Average Loans to Money Pool					189.4
Net Loans (Borrowings) to/from Money Pool			$ (213.9)		(213.9)
Authorized Short Term Borrowing Limit					$ 500.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.24%	1.31%
Average Interest Rate For Funds Loaned					2.47%	0.98%
Ohio Power Co [Member] | Securitization Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 22.9
Interest Rate (Percentage)			2.049%		2.049%
Due Date					2019
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 22.9
Ohio Power Co [Member] | Securitization Bonds [Member] | Subsequent Event [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments		24.0
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt		$ 24.0
Ohio Power Co [Member] | Senior Unsecured Notes [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 400.0
Interest Rate (Percentage)			4.15%		4.15%
Due Date					2048
Ohio Power Co [Member] | Senior Unsecured Notes Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 350.0
Interest Rate (Percentage)			6.05%		6.05%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 350.0
Public Service Co Of Oklahoma [Member]
Long-term Debt
Total Long-term Debt Outstanding			$ 1,286.8		1,286.8		1,286.5
Long-term Debt Due Within One Year			0.5		0.5		0.5
Long-term Debt			1,286.3		1,286.3		1,286.0
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					0.2	$ 0.2
Accounts Receivable and Accrued Unbilled Revenues
Accounts Receivable and Accrued Unbilled Revenues			159.1		159.1		115.1
Fees Paid to AEP Credit for Customer Accounts Receivable Sold
Fees Paid to AEP Credit for Customer Accounts Receivable Sold			1.9	1.7	3.7	3.2
Proceeds from Sale of Receivables
Proceeds from Sale of Receivables to AEP Credit			383.7	328.7	716.4	615.5
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 0.2	$ 0.2
Maximum Percentage Debt to Capitalization					67.50%
Public Service Co Of Oklahoma [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 193.7
Maximum Loans to Money Pool					0.0
Average Borrowings from Money Pool					149.4
Average Loans to Money Pool					0.0
Net Loans (Borrowings) to/from Money Pool			$ (118.4)		(118.4)
Authorized Short Term Borrowing Limit					$ 300.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.24%	1.23%
Average Interest Rate For Funds Loaned					0.00%	0.00%
Public Service Co Of Oklahoma [Member] | Other Long Term Debt [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 0.2
Interest Rate (Percentage)			3.00%		3.00%
Due Date					2027
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 0.2
Southwestern Electric Power Co [Member]
Long-term Debt
Total Long-term Debt Outstanding			$ 2,503.7		2,503.7		2,441.9
Long-term Debt Due Within One Year			457.2		457.2		3.7
Long-term Debt			2,046.5		2,046.5		2,438.2
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					383.5	$ 351.8
Short-term Debt:
Notes Payable			25.2		25.2		22.0
Accounts Receivable and Accrued Unbilled Revenues
Accounts Receivable and Accrued Unbilled Revenues			188.9		188.9		$ 138.2
Fees Paid to AEP Credit for Customer Accounts Receivable Sold
Fees Paid to AEP Credit for Customer Accounts Receivable Sold			2.1	1.8	4.0	3.4
Proceeds from Sale of Receivables
Proceeds from Sale of Receivables to AEP Credit			454.5	$ 404.6	852.0	745.8
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 383.5	$ 351.8
Maximum Percentage Debt to Capitalization					67.50%
Southwestern Electric Power Co [Member] | Utility [Member]
Maximum Interest Rate					2.52%	1.44%
Minimum Interest Rate					1.83%	0.92%
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Borrowings from Money Pool					$ 200.1
Maximum Loans to Money Pool					296.5
Average Borrowings from Money Pool					164.2
Average Loans to Money Pool					273.2
Net Loans (Borrowings) to/from Money Pool			(119.9)		(119.9)
Authorized Short Term Borrowing Limit					$ 350.0
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Borrowed					2.34%	1.20%
Average Interest Rate For Funds Loaned					1.88%	0.98%
Southwestern Electric Power Co [Member] | Nonutility [Member]
Money Pool Participants Money Pool Activity And Authorized Borrowing Limits [Abstract]
Maximum Loans to Money Pool					$ 2.0
Average Loans to Money Pool					2.0
Net Loans (Borrowings) to/from Money Pool			$ 2.0		$ 2.0
Maximum and Minimum Interest Rates
Maximum Interest Rate For Funds Loaned					2.52%	1.44%
Minimum Interest Rate for Funds Loaned					1.83%	0.00%
Average Interest Rates for Funds Borrowed From and Loaned to Money Pool [Abstract]
Average Interest Rate For Funds Loaned					2.23%	1.17%
Southwestern Electric Power Co [Member] | Notes Payable, Other Payables [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 1.6
Interest Rate (Percentage)			4.58%		4.58%
Due Date					2032
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 1.6
Southwestern Electric Power Co [Member] | Other Long Term Debt [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 0.1
Interest Rate (Percentage)			3.50%		3.50%
Due Date					2023
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 0.1
Southwestern Electric Power Co [Member] | Other Long Term Debt Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 0.1
Interest Rate (Percentage)			4.28%		4.28%
Due Date					2023
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 0.1
Southwestern Electric Power Co [Member] | Pollution Control Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 81.7
Interest Rate (Percentage)			4.95%		4.95%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 81.7
Southwestern Electric Power Co [Member] | Senior Unsecured Notes [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 450.0
Interest Rate (Percentage)			3.85%		3.85%
Due Date					2048
Southwestern Electric Power Co [Member] | Senior Unsecured Notes Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 300.0
Interest Rate (Percentage)			5.875%		5.875%
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 300.0
Southwestern Electric Power Co [Member] | Loans Payable [Member]
Short-term Debt:
Weighted Average Interest Rate	[4]		3.35%		3.35%		2.92%
Transource Energy [Member] | Other Long Term Debt [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 8.7
Interest Rate (Variable)					Variable
Due Date					2020
Wheeling Power Co [Member] [Domain] | Pollution Control Bonds [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Issuances	[2]				$ 65.0
Interest Rate (Percentage)			3.00%		3.00%
Due Date					2022
Wheeling Power Co [Member] [Domain] | Pollution Control Bonds Two [Member]
Long-term Debt and Other Securities Issued, Retired and Principal Payments Made
Retirements and Principal Payments					$ 65.0
Interest Rate (Variable)					Variable
Due Date					2018
Financing Activities (Textuals) [Abstract]
Repayments of Long-term Debt					$ 65.0

[1] Pursuant to the Nuclear Waste Policy Act of 1982, I&M, a nuclear licensee, has an obligation to the United States Department of Energy for spent nuclear fuel disposal. The obligation includes a one-time fee for nuclear fuel consumed prior to April 7, 1983. Trust fund assets related to this obligation were $314 million and $312 million as of June 30, 2018 and December 31, 2017, respectively, and are included in Spent Nuclear Fuel and Decommissioning Trusts on the balance sheets.

[2] Amounts indicated on the statements of cash flows are net of issuance costs and premium or discount and will not tie to the issuance amounts.

[3] Amount of securitized debt for receivables as accounted for under the “Transfers and Servicing” accounting guidance.

[4] Weighted average rate.

[5] Amount represents the combined authorized short-term borrowing limit the State Transcos have from FERC or state regulatory commissions.

[6] Amount represents the combined authorized short-term borrowing limit the State Transcos have from FERC or state regulatory commissions.