Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2017

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory Assets

Regulatory assets were comprised of the following items:

At December 31, (in millions)	2017		2016
Regulatory Assets
Unrecognized pension and other postretirement benefit costs (see Note 11)	$	733.5	$	847.5
Deferred pension and other postretirement benefit costs (see Note 11)	70.7		59.6
Environmental costs (see Note 18-D)	63.4		62.6
Regulatory effects of accounting for income taxes (see Note 1-O and Note 10)	238.8		238.4
Underrecovered gas and fuel costs (see Note 1-K)	25.5		73.5
Depreciation	181.0		187.1
Post-in-service carrying charges	173.3		142.0
Safety activity costs	66.5		41.5
DSM programs	40.0		48.4
Other	208.5		184.8
Total Regulatory Assets	$	1,801.2	$	1,885.4

Regulatory Liabilities

Regulatory liabilities were comprised of the following items:

At December 31, (in millions)	2017		2016
Regulatory Liabilities
Overrecovered gas and fuel costs (see Note 1-K)	$	27.6	$	54.8
Cost of removal (see Note 7)	1,096.8		1,174.5
Regulatory effects of accounting for income taxes (see Note 1-O and Note 10)	1,563.4		30.0
Deferred pension and other postretirement benefit costs (see Note 11)	59.0		41.2
Other	48.8		81.3
Total Regulatory Liabilities	$	2,795.6	$	1,381.8