Income Taxes Income Taxes (Effect of Rate-making On Property-related Differences) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Effect of Rate-making on Property-related Differences [Line Items]
Income tax rates for continuing operations	13.30%	19.50%	13.00%	28.30%
Effect of Rate-making On Property-related Differences [Member]
Effect of Rate-making on Property-related Differences [Line Items]
Income tax rates for continuing operations	(6.40%)	(4.00%)	(5.60%)	(3.60%)
IPL [Member]
Effect of Rate-making on Property-related Differences [Line Items]
Income tax rates for continuing operations	(24.70%)	(12.00%)	(24.30%)	22.60%
IPL [Member] | Effect of Rate-making On Property-related Differences [Member]
Effect of Rate-making on Property-related Differences [Line Items]
Income tax rates for continuing operations	(17.40%)	(8.10%)	(15.50%)	(7.70%)