Fair Value Measurements (Narrative) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
5.1% [Member] \| Redeemable Preferred Stock [Member] \| IPL [Member]
Cumulative preferred stock rate	5.10%	5.10%

The percentage rate used to calculate dividend payments on preferred stock.

No definition available.

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration