XML 119 R88.htm IDEA: XBRL DOCUMENT v3.19.2
Related Party Transactions - Payables Due To/From Related Parties (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Tax Allocation Agreement | AEP    
Related Party Transaction [Line Items]    
Accounts Receivable (Payable) $ 4 $ 5