Income Taxes
 12 Months Ended
Dec. 31, 2015
Income Tax Disclosure [Abstract]  
Income Taxes
Income Taxes
The components of income tax expense were as follows:
Year Ended December 31, (in millions)
2015
 
2014
 
2013
 
 
 
Predecessor
 
Predecessor
Income Taxes
 
 
 
 
 
Current
 
 
 
 
 
Federal
$
12.0

 
$
21.3

 
$
(16.1
)
State
1.2

 
5.8

 
(11.4
)
Total Current
13.2

 
27.1

 
(27.5
)
Deferred
 
 
 
 
 
Federal
8.8

 
117.7

 
155.9

State
1.9

 
21.7

 
24.1

Total Deferred
10.7

 
139.4

 
180.0

Deferred Investment Credits
—

 
(0.1
)
 
(0.1
)
Total Income Taxes
$
23.9

 
$
166.4

 
$
152.4


Total income taxes were different from the amount that would be computed by applying the statutory federal income tax rate to book income before income tax. The major reasons for this difference were as follows:
Year Ended December 31, (in millions)
2015
 
2014
 
2013
 
 
 
 
 
Predecessor
 
Predecessor
Book income before income taxes
$
554.1

 
 
 
$
435.5

 
 
 
$
419.3

 
 
Tax expense at statutory federal income tax rate
193.9

 
35.0
 %
 
152.4

 
35.0
 %
 
146.8

 
35.0
 %
Increases (reductions) in taxes resulting from:
 
 
 
 
 
 
 
 
 
 
 
State income taxes, net of federal income tax benefit
2.0

 
0.4

 
17.9

 
4.1

 
8.2

 
1.9

Income not subject to income tax at the partnership level
(170.6
)
 
(30.9
)
 
—

 
—

 
—

 
—

AFUDC-Equity
(0.3
)
 
—

 
(3.8
)
 
(0.9
)
 
(2.4
)
 
(0.6
)
Other, net
(1.1
)
 
(0.2
)
 
(0.1
)
 
—

 
(0.2
)
 
—

Total Income Taxes
$
23.9

 
4.3
 %
 
$
166.4

 
38.2
 %
 
$
152.4

 
36.3
 %

The effective income tax rates were 4.3%, 38.2%, and 36.3% in 2015, 2014 and 2013, respectively. The effective tax rate for 2015 differs from the federal tax rate of 35% primarily due to the income received following the Partnership's IPO that is not subject to income tax at the partnership level. The effective tax rate is impacted by the Partnership’s IPO which modified the ownership structure and now reflects Partnership earnings for which the noncontrolling public limited partners are directly responsible for the related income taxes.
The effective tax rate for 2014 and 2013 differs from the Federal tax rate of 35% primarily due to the effects of tax credits, state income taxes, utility rate-making, as well as other permanent book-to-tax differences.
Net earnings for financial statement purposes may differ significantly from taxable income reportable to unitholders as a result of differences between the tax basis and financial basis of assets and liabilities, differences between the tax accounting and financial accounting treatment of certain items.
The Partnership had no unrecognized tax benefits related to uncertain tax positions as of December 31, 2015. As of December 31, 2014 and 2013, the Predecessor financial statements included unrecognized tax benefits of zero and $0.1 million, respectively.
Deferred income taxes result from temporary differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities.
The principal components of the Partnership’s net deferred tax liability were as follows:
At December 31, (in millions)
2015
 
2014
 
 
 
Predecessor
Deferred tax liabilities
 
 
 
Accelerated depreciation and other property differences
$
1.0

 
$
1,235.3

Pension and other postretirement/postemployment benefits
—

 
24.3

Other regulatory assets
—

 
62.8

Other, net
—

 
77.9

Total Deferred Tax Liabilities
1.0

 
1,400.3

Deferred tax assets
 
 
 
Deferred investment tax credits and other regulatory liabilities
—

 
(116.7
)
Net operating loss carryforward and AMT credit carryforward
—

 
(67.8
)
Other accrued liabilities
—

 
(1.4
)
Total Deferred Tax Assets
—

 
(185.9
)
Net Deferred Tax Liabilities less Deferred Tax Assets
1.0

 
1,214.4

Less: Deferred income taxes related to current assets and liabilities
—

 
(24.6
)
Non-Current Deferred Tax Liabilities
$
1.0

 
$
1,239.0