Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Receivables [Line Items]
Fair value of deferred proceeds	$ 208.3	$ 222.1
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	208.3	222.1
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	155.7	133.8
Unbilled utility revenues	93.9	112.7
Other receivables	0.4	0.3
Receivables sold to third party	250.0	246.8
Less: cash proceeds	29.0	12.0
Deferred proceeds	221.0	234.8
Less: allowance for doubtful accounts	12.7	12.7
Fair value of deferred proceeds	$ 208.3	$ 222.1