Variable Interest Entities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jun. 30, 2018 USD ($) MW	Dec. 31, 2017 USD ($)
Variable Interest Entities (Textuals) [Abstract]
Redeemable Noncontrolling Interest		$ 70.4	$ 0.0
Trent and Desert Sky Wind Farms [Member]
Variable Interest Entities (Textuals) [Abstract]
Wind Generation (MWs) | MW		310.5
Non-Affiliate Interest		20.10%
AEP Ownership in LLCs		79.90%
Desert Sky and Trent PPA Period	12 years
Redeemable Noncontrolling Interest		$ 70.0
Current Assets [Member] | Trent and Desert Sky Wind Farms [Member]
Assets [Abstract]
Assets		46.6
Net Property Plant And Equipment [Member] | Trent and Desert Sky Wind Farms [Member]
Assets [Abstract]
Assets		313.6
Net Property Plant And Equipment [Member] | Non-Affiliate Contribution [Member]
Assets [Abstract]
Assets		84.0
Other Noncurrent Assets [Member] | Trent and Desert Sky Wind Farms [Member]
Assets [Abstract]
Assets		0.7
Total Assets [Member] | Trent and Desert Sky Wind Farms [Member]
Assets [Abstract]
Assets		360.9
Current Liabilities [Member] | Trent and Desert Sky Wind Farms [Member]
Liabilities and Equity [Abstract]
Variable Interest Carrying Amount Liabilities and Equity		101.0
Noncurrent Liabilities [Member] | Trent and Desert Sky Wind Farms [Member]
Liabilities and Equity [Abstract]
Variable Interest Carrying Amount Liabilities and Equity		6.0
Equity [Member] | Trent and Desert Sky Wind Farms [Member]
Liabilities and Equity [Abstract]
Variable Interest Carrying Amount Liabilities and Equity		253.9
Total Liabilities And Equity [Member] | Trent and Desert Sky Wind Farms [Member]
Liabilities and Equity [Abstract]
Variable Interest Carrying Amount Liabilities and Equity		$ 360.9