Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable [Line Items]
Fair value of deferred proceeds	$ 187.7	$ 119.4
IPL [Member]
Accounts Receivable [Line Items]
Fair value of deferred proceeds	187.7	119.4
Financing Receivable [Member] | IPL [Member]
Accounts Receivable [Line Items]
Customer accounts receivable	124.7	140.1
Unbilled utility revenues	95.5	97.1
Other receivables	0.9	0.1
Receivables sold to third party	221.1	237.3
Less: cash proceeds	27.0	108.0
Deferred proceeds	194.1	129.3
Less: allowance for doubtful accounts	6.4	9.9
Fair value of deferred proceeds	187.7	119.4
Outstanding receivables, past due	$ 26.0	$ 35.5