Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable [Line Items]
Fair value of deferred proceeds	$ 119.4	$ 222.1
IPL [Member]
Accounts Receivable [Line Items]
Fair value of deferred proceeds	119.4	222.1
Receivables Sold [Member] | IPL [Member]
Accounts Receivable [Line Items]
Customer accounts receivable	140.1	133.8
Unbilled utility revenues	97.1	112.7
Other receivables	0.1	0.3
Receivables sold to third party	237.3	246.8
Less: cash proceeds	108.0	12.0
Deferred proceeds	129.3	234.8
Less: allowance for doubtful accounts	9.9	12.7
Fair value of deferred proceeds	119.4	222.1
Outstanding receivables past due	$ 35.5	$ 44.7