Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 2015	Dec. 31, 2015
Variable Interest Entities (Textuals) [Abstract]
Securitization Bonds	$ 1,737.6			$ 1,737.6			$ 2,024.0
Securitized Transition Assets	1,559.0			$ 1,559.0			1,749.9
Percentage of Ownership of Allegheny Series by a Nonaffiliated Company				100.00%
Protected Cell Of Energy Insurance Services, Inc. [Member]
Variable Interest Entities (Textuals) [Abstract]
Insurance Premium Expense to Protected Cell	15.0		$ 13.0	$ 28.0		$ 27.0
Protected Cell Of Energy Insurance Services, Inc. [Member] | Current Assets [Member]
ASSETS
Assets	179.4			179.4			165.3
Protected Cell Of Energy Insurance Services, Inc. [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	0.0			0.0			0.0
Protected Cell Of Energy Insurance Services, Inc. [Member] | Other Non Current Assets [Member]
ASSETS
Assets	1.7			1.7			1.9
Protected Cell Of Energy Insurance Services, Inc. [Member] | Total Assets [Member]
ASSETS
Assets	181.1			181.1			167.2
Protected Cell Of Energy Insurance Services, Inc. [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	47.7			47.7			41.8
Protected Cell Of Energy Insurance Services, Inc. [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	91.1			91.1			83.9
Protected Cell Of Energy Insurance Services, Inc. [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	42.3			42.3			41.5
Protected Cell Of Energy Insurance Services, Inc. [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	181.1			181.1			167.2
Transource Energy [Member]
Variable Interest Entities (Textuals) [Abstract]
Proceeds from Partnership Contribution				38.0			47.0
Transource Energy [Member] | Current Assets [Member]
ASSETS
Assets	12.2			12.2			10.8
Transource Energy [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	298.5			298.5			227.2
Transource Energy [Member] | Other Non Current Assets [Member]
ASSETS
Assets	5.5			5.5			5.5
Transource Energy [Member] | Total Assets [Member]
ASSETS
Assets	316.2			316.2			243.5
Transource Energy [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	35.4			35.4			36.6
Transource Energy [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	127.2			127.2			113.0
Transource Energy [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	153.6			153.6			93.9
Transource Energy [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	316.2			$ 316.2			243.5
AEP Credit, Inc. [Member]
Variable Interest Entities (Textuals) [Abstract]
Minimum Percentage of Equity AEP Provides				5.00%
Percentage of Short Term Borrowing Needs in Excess of Third Party Financings				20.00%
AEP Credit, Inc. [Member] | Current Assets [Member]
ASSETS
Assets	1,038.7			$ 1,038.7			925.7
AEP Credit, Inc. [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	0.0			0.0			0.0
AEP Credit, Inc. [Member] | Other Non Current Assets [Member]
ASSETS
Assets	10.3			10.3			6.4
AEP Credit, Inc. [Member] | Total Assets [Member]
ASSETS
Assets	1,049.0			1,049.0			932.1
AEP Credit, Inc. [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	948.2			948.2			855.1
AEP Credit, Inc. [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	0.6			0.6			0.3
AEP Credit, Inc. [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	100.2			100.2			76.7
AEP Credit, Inc. [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	$ 1,049.0			$ 1,049.0			932.1
PATH West Virginia Transmission Co, LLC [Member]
Variable Interest Entities (Textuals) [Abstract]
Percentage of Debt Capital Structure in PATH's Stipulation Agreement	50.00%			50.00%
Percentage of Equity Capital Structure in PATH's Stipulation Agreement	50.00%			50.00%
Percentage of Cost of Long Term Debt for PATH's Stipulation Agreement	4.70%			4.70%
PATH West Virginia Transmission Co, LLC [Member] | Capital Contribution From Parent [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	$ 18.8			$ 18.8			18.8
Maximum Exposure	18.8			18.8			18.8
PATH West Virginia Transmission Co, LLC [Member] | Retained Earnings [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	2.2			2.2			2.2
Maximum Exposure	2.2			2.2			2.2
PATH West Virginia Transmission Co, LLC [Member] | Total Investment [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	21.0			21.0			21.0
Maximum Exposure	21.0			21.0			21.0
AEP Texas Central Transition Funding Co [Member]
Variable Interest Entities (Textuals) [Abstract]
Securitization Bonds	1,300.0			1,300.0			1,500.0
Securitized Transition Assets	1,100.0			1,100.0			1,300.0
AEP Texas Central Transition Funding Co [Member] | Current Assets [Member]
ASSETS
Assets	163.5			163.5			234.1
AEP Texas Central Transition Funding Co [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	0.0			0.0			0.0
AEP Texas Central Transition Funding Co [Member] | Other Non Current Assets [Member]
ASSETS
Assets	1,210.4	[1]		1,210.4	[1]		1,365.7	[2]
Variable Interest Entities (Textuals) [Abstract]
Intercompany Item Eliminated in Consolidation	62.9			62.9			68.2
AEP Texas Central Transition Funding Co [Member] | Total Assets [Member]
ASSETS
Assets	1,373.9			1,373.9			1,599.8
AEP Texas Central Transition Funding Co [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	242.6			242.6			291.7
AEP Texas Central Transition Funding Co [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	1,113.2			1,113.2			1,290.0
AEP Texas Central Transition Funding Co [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	18.1			18.1			18.1
AEP Texas Central Transition Funding Co [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	$ 1,373.9			$ 1,373.9			1,599.8
Great Plains Energy Inc. [Member] | Transource Energy [Member]
Variable Interest Entities (Textuals) [Abstract]
Equity and Voting Ownership Percentage	13.50%			13.50%
Cleco Power, LLC [Member]
Variable Interest Entities (Textuals) [Abstract]
Percentage of VIE Sales of Lignite Produced				50.00%
Appalachian Power Co [Member]
Variable Interest Entities (Textuals) [Abstract]
Securitized Transition Assets	$ 311.0			$ 311.0			328.0
Appalachian Power Co [Member] | Billings from AEP Service Corporation [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	55.3		63.7	165.7		164.7
Appalachian Power Co [Member] | Carrying Amount in AEP Service Corporation's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	20.0			20.0			25.8
Maximum Exposure	20.0			20.0			25.8
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member]
Variable Interest Entities (Textuals) [Abstract]
Securitization Bonds	319.0			319.0			342.0
Securitized Transition Assets	311.0			311.0			328.0
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Current Assets [Member]
ASSETS
Assets	11.8			11.8			18.5
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	0.0			0.0			0.0
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Other Non Current Assets [Member]
ASSETS
Assets	314.7	[3]		314.7	[3]		332.0	[4]
Variable Interest Entities (Textuals) [Abstract]
Intercompany Item Eliminated in Consolidation	3.8			3.8			4.0
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Total Assets [Member]
ASSETS
Assets	326.5			326.5			350.5
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	25.0			25.0			27.1
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	300.2			300.2			321.5
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	1.3			1.3			1.9
Appalachian Power Co [Member] | Appalachian Consumer Rate Relief Funding [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	326.5			326.5			350.5
Indiana Michigan Power Co [Member] | DCC Fuel [Member]
Variable Interest Entities (Textuals) [Abstract]
Payments Made by I&M to DCC Fuel	23.0		29.0	77.0		86.0
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Current Assets [Member]
ASSETS
Assets	109.2			109.2			91.1
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	165.9			165.9			159.9
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Other Non Current Assets [Member]
ASSETS
Assets	78.8			78.8			84.6
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Total Assets [Member]
ASSETS
Assets	353.9			353.9			335.6
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	98.2			98.2			84.8
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	255.7			255.7			250.8
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	0.0			0.0			0.0
Indiana Michigan Power Co [Member] | DCC Fuel [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	353.9			353.9			335.6
Indiana Michigan Power Co [Member] | Billings from AEP Service Corporation [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	32.7		37.5	97.7		102.1
Indiana Michigan Power Co [Member] | Billings from AEP Generating Company [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	65.0		67.0	166.0		182.0
Indiana Michigan Power Co [Member] | Carrying Amount in AEP Service Corporation's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	11.0			11.0			16.6
Maximum Exposure	11.0			11.0			16.6
Indiana Michigan Power Co [Member] | Carrying Amount in AEP Generating Company's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	17.0			17.0			17.0
Ohio Power Co [Member]
Variable Interest Entities (Textuals) [Abstract]
Securitized Transition Assets	68.0			68.0			85.9
Ohio Power Co [Member] | Billings from AEP Service Corporation [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	39.4		48.5	123.2		128.6
Ohio Power Co [Member] | Carrying Amount in AEP Service Corporation's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	13.9			13.9			23.3
Maximum Exposure	13.9			13.9			23.3
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member]
Variable Interest Entities (Textuals) [Abstract]
Securitization Bonds	140.0			140.0			185.0
Securitized Transition Assets	68.0			68.0			86.0
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Current Assets [Member]
ASSETS
Assets	18.9			18.9			31.2
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	0.0			0.0			0.0
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Other Non Current Assets [Member]
ASSETS
Assets	128.1	[5]		128.1	[5]		162.0	[6]
Variable Interest Entities (Textuals) [Abstract]
Intercompany Item Eliminated in Consolidation	60.2			60.2			76.1
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Total Assets [Member]
ASSETS
Assets	147.0			147.0			193.2
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	46.9			46.9			47.3
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	98.8			98.8			144.6
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	1.3			1.3			1.3
Ohio Power Co [Member] | Ohio Phase-In-Recovery Funding [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	147.0			147.0			193.2
Public Service Co Of Oklahoma [Member] | Billings from AEP Service Corporation [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	23.6		29.9	77.1		77.8
Public Service Co Of Oklahoma [Member] | Carrying Amount in AEP Service Corporation's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	7.8			7.8			12.6
Maximum Exposure	7.8			7.8			12.6
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	42.0		41.0	127.0		124.0
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Current Assets [Member]
ASSETS
Assets	61.8			61.8			61.7
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Net Property Plant And Equipment [Member]
ASSETS
Assets	123.6			123.6			147.0
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Other Non Current Assets [Member]
ASSETS
Assets	63.9			63.9			61.8
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Total Assets [Member]
ASSETS
Assets	249.3			249.3			270.5
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Current Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	32.0			32.0			47.7
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Noncurrent Liabilities [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	217.0			217.0			222.3
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	0.3			0.3			0.5
Southwestern Electric Power Co [Member] | Sabine Mining Co [Member] | Total Liabilities And Equity [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	249.3			249.3			270.5
Southwestern Electric Power Co [Member] | Dolet Hills Lignite Co, LLC [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	20.3			20.3			15.3
Maximum Exposure	113.0			113.0			98.2
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	15.0		30.0	$ 43.0		59.0
Percentage of VIE Sales of Lignite Produced				50.00%
Percentage of DHLCs Debt Guaranteed by Each SWEPCo and CLECO				50.00%
Percentage Of Management Fee Received by SWEPCo from DHLC				100.00%
Southwestern Electric Power Co [Member] | Dolet Hills Lignite Co, LLC [Member] | Capital Contribution From Parent [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	7.6			$ 7.6			7.6
Maximum Exposure	7.6			7.6			7.6
Southwestern Electric Power Co [Member] | Dolet Hills Lignite Co, LLC [Member] | Retained Earnings [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	12.7			12.7			7.7
Maximum Exposure	12.7			12.7			7.7
Southwestern Electric Power Co [Member] | Dolet Hills Lignite Co, LLC [Member] | SWEPCo's Guarantee Of Debt [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	0.0			0.0			0.0
Maximum Exposure	92.7			92.7			82.9
Southwestern Electric Power Co [Member] | Billings from AEP Service Corporation [Member]
Variable Interest Entities (Textuals) [Abstract]
Billings from VIE	31.4		$ 39.2	101.2		$ 102.6
Southwestern Electric Power Co [Member] | Carrying Amount in AEP Service Corporation's Accounts Payable [Member]
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
As Reported on the Consolidated Balance Sheet	11.8			11.8			16.4
Maximum Exposure	$ 11.8			$ 11.8			$ 16.4
AEP Generating Co [Member] | Rockport Generating Plant (Unit No. 1) [Member]
Variable Interest Entities (Textuals) [Abstract]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%			50.00%
AEP Generating Co [Member] | Rockport Generating Plant (Unit No. 2) [Member]
Variable Interest Entities (Textuals) [Abstract]
Percentage Interest in Rockport Plant Unit 2 Lease	50.00%			50.00%
AEP Generating Co [Member] | Lawrenceburg Generating Station [Member]
Variable Interest Entities (Textuals) [Abstract]
Jointly Owned Utility Plant, Proportionate Ownership Share	100.00%			100.00%
Transource Energy [Member]
Variable Interest Entities (Textuals) [Abstract]
Equity and Voting Ownership Percentage	86.50%			86.50%

[1] Includes an intercompany item eliminated in consolidation of $62.9 million.

[2] Includes an intercompany item eliminated in consolidation of $68.2 million.

[3] Includes an intercompany item eliminated in consolidation of $3.8 million.

[4] Includes an intercompany item eliminated in consolidation of $4.0 million.

[5] Includes an intercompany item eliminated in consolidation of $60.2 million.

[6] Includes an intercompany item eliminated in consolidation of $76.1 million.