Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Reconciliation of the Federal Statutory Rate to Effective Income Tax Rate

A reconciliation of the federal statutory rate to the effective income tax rate follows:

	Year Ended December 31,
	2017		2016		2015
Statutory rate:	35.0	%	35.0	%	35.0	%
State & local taxes-net of federal benefit	3.4		2.8		3.6
Deferred tax revaluation-tax law change	(17.3	)	—		—
Amortization of investment tax credit	(0.2	)	(0.3	)	(0.2	)
Domestic production deduction	(1.4	)	(0.4	)	(1.0	)
Energy efficiency building deductions	—		(1.7	)	(2.3	)
Research and development credit	(0.3	)	(0.6	)	(1.6	)
Other tax credits	(0.1	)	(0.1	)	(0.1	)
All other-net	(1.4	)	0.1		0.2
Effective tax rate	17.7	%	34.8	%	33.6	%

Significant Components of Net Deferred Tax Liability

Significant components of the net deferred tax liability follow:

	At December 31,
(In millions)	2017			2016
Noncurrent deferred tax liabilities (assets):
Depreciation & cost recovery timing differences	$	593.7		$	902.4
Regulatory assets recoverable through future rates	7.9			17.6
Alternative minimum tax carryforward	(12.2		)	(29.3		)
Employee benefit obligations	(9.3		)	(8.1		)
Net operating loss & other carryforwards (net of valuation allowances)	(4.1		)	(3.2		)
U.S. federal charitable contributions carryforwards	(12.2		)	—
Regulatory liabilities to be settled through future rates	(116.2		)	(15.9		)
Impairments	(0.6		)	(2.5		)
Deferred fuel costs-net	16.2			25.9
Other-net	28.1			18.8
Net noncurrent deferred tax liability	$	491.3		$	905.7

Components of Income Tax Expense

The components of income tax expense follow:

	Year Ended December 31,
(In millions)	2017			2016			2015
Current:
Federal	$	20.5		$	6.8		$	10.8
State	6.9			6.0			8.5
Total current taxes	27.4			12.8			19.3
Deferred:
Federal	16.7			97.6			79.0
State	2.7			3.6			2.0
Total deferred taxes	19.4			101.2			81.0
Amortization of investment tax credits	(0.4		)	(1.1		)	(0.6		)
Total income tax expense	$	46.4		$	112.9		$	99.7