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Pension and Other Post-Retirement Benefits
 3 Months Ended
Mar. 31, 2016
Compensation and Retirement Disclosure [Abstract]  
Pension and Other Post-Retirement Benefits
Pension and Other Post-Retirement Benefits

The following table shows components of our pension and other post-retirement benefits expense for the three months ended March 31, 2016 and 2015 (in millions):
 
2016 Pension
Benefits
 
2015 Pension
Benefits
 
2016 Retiree
Health
and Life
 
2015 Retiree
Health
and Life
Service cost
$
1.6

 
$
1.7

 
$
—

 
$
—

Interest cost
3.9

 
4.9

 
0.3

 
0.4

Expected return on plan assets
(6.5
)
 
(6.5
)
 
—

 
—

Amortization of (1):
 
 
 
 
 
 
 
Unrecognized prior service credit
(0.2
)
 
(0.2
)
 
(0.1
)
 
—

Unrecognized net actuarial loss
2.6

 
3.5

 
—

 
—

Net expense
$
1.4

 
$
3.4

 
$
0.2

 
$
0.4

_________
(1) Amounts reclassified from accumulated other comprehensive loss.

The decrease in pension expense was primarily due to a prospective change in accounting estimate. See "Note 2. Basis of Presentation" for further details about this change in accounting estimate.