Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Receivables [Line Items]
Fair value of deferred proceeds	$ 178.3	$ 119.4
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	178.3	119.4
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	169.9	140.1
Unbilled utility revenues	86.8	97.1
Other receivables	0.1	0.1
Receivables sold to third party	256.8	237.3
Less: cash proceeds	69.0	108.0
Deferred proceeds	187.8	129.3
Less: allowance for doubtful accounts	9.5	9.9
Fair value of deferred proceeds	$ 178.3	$ 119.4