Variable Interest Entities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) MW	Dec. 31, 2017 USD ($)
Variable Interest Entities (Textuals) [Abstract]
Redeemable Noncontrolling Interest	$ 70.7	$ 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	$ 71.0
Current Assets [Member] | Trent and Desert Sky Wind Farms [Member]
ASSETS
Assets	41.1
Net Property Plant And Equipment [Member] | Trent and Desert Sky Wind Farms [Member]
ASSETS
Assets	255.4
Net Property Plant And Equipment [Member] | Non-Affiliate Contribution [Member]
ASSETS
Assets	84.0
Other Noncurrent Assets [Member] | Trent and Desert Sky Wind Farms [Member]
ASSETS
Assets	0.7
Total Assets [Member] | Trent and Desert Sky Wind Farms [Member]
ASSETS
Assets	297.2
Current Liabilities [Member] | Trent and Desert Sky Wind Farms [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	41.4
Noncurrent Liabilities [Member] | Trent and Desert Sky Wind Farms [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	8.3
Equity [Member] | Trent and Desert Sky Wind Farms [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	247.5
Total Liabilities And Equity [Member] | Trent and Desert Sky Wind Farms [Member]
LIABILITIES AND EQUITY
Liabilities and Equity	$ 297.2