Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2012

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory Assets

Regulatory assets were comprised of the following items:

At December 31, (in millions)	2012			2011
Assets
Reacquisition premium on debt	$	8.6		$	10.9
R. M. Schahfer Unit 17 and Unit 18 carrying charges and deferred depreciation (see Note 1-H)	5.5			8.7
Unrecognized pension benefit and other postretirement benefit costs (see Note 12)	1,345.7			1,244.2
Other postretirement costs	66.3			76.1
Environmental costs (see Note 20-D)	77.5			84.7
Regulatory effects of accounting for income taxes (see Note 1-V)	245.7			254.5
Underrecovered gas and fuel costs (see Note 1-P and 1-Q)	45.0			20.7
Depreciation (see Note 1-H)	113.9			115.4
Uncollectible accounts receivable deferred for future recovery	6.1			8.0
Asset retirement obligations (see Note 7)	16.1			14.4
Losses on derivatives (see Note 9)	17.1			44.7
Post-in-service carrying charges	61.2			51.6
EERM operation and maintenance and depreciation deferral	9.8			37.4
MISO (see Note 8)	28.8			42.4
Sugar Creek carrying charges and deferred depreciation (see Note 1-H)	71.2			85.5
Other	113.7			69.4
Total Assets	$	2,232.2		$	2,168.6
Less amounts included as Underrecovered gas and fuel cost	(45.0		)	(20.7		)
Total Regulatory Assets reflected in Current Regulatory Assets and Other Regulatory Assets	$	2,187.2		$	2,147.9

Regulatory Liabilities

Regulatory liabilities were comprised of the following items:

At December 31, (in millions)	2012			2011
Liabilities
Overrecovered gas and fuel costs (see Notes 1-P and 1-Q)	$	22.1		$	48.9
Cost of removal (see Note 7)	1,437.5			1,476.5
Regulatory effects of accounting for income taxes (see Note 1-V)	76.9			109.3
Other postretirement costs	97.4			95.7
Percentage of income plan	16.0			12.0
Off-system sales margin sharing	5.8			5.1
Emission allowances (see Note 8)	0.8			7.4
Other	130.5			69.9
Total Liabilities	$	1,787.0		$	1,824.8
Less amounts included as Overrecovered gas and fuel cost	(22.1		)	(48.9		)
Total Regulatory Liabilities reflected in Current Regulatory Liabilities and Other Regulatory Liabilities and Other Removal Costs	$	1,764.9		$	1,775.9