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Pension and Other Postretirement Benefits (Notes)
 3 Months Ended
Mar. 31, 2016
General Discussion of Pension and Other Postretirement Benefits [Abstract]  
Pension and Other Postretirement Benefits
Pension and Other Postretirement Benefits
 

We provide noncontributory pension and various healthcare and life insurance benefits to most employees and retirees. No contributions to the master pension trust are required for 2016. Based on current actuarial assumptions, we estimate that our required pension contributions will be approximately $50.0 and $75.0 in 2017 and 2018, though the amounts we will be required to pay are more dependent on plan asset returns than in the past. Other factors which affect future funding projections, in addition to differences between expected and actual returns on plan assets, are actuarial data and assumptions relating to plan participants, the interest rate used to measure the pension obligations and changes to regulatory funding requirements.

Net periodic benefit cost (income) for pension and other postretirement benefits was as follows:
 
Three Months Ended March 31,
 
2016
 
2015
Pension Benefits
 
 
 
Service cost
$
0.7

 
$
0.6

Interest cost
32.0

 
32.5

Expected return on assets
(42.9
)
 
(49.7
)
Amortization of prior service cost
1.3

 
1.1

Amortization of loss
7.0

 
7.8

Net periodic benefit cost (income)
$
(1.9
)
 
$
(7.7
)
 
 
 
 
Other Postretirement Benefits
 
 
 
Service cost
$
1.2

 
$
1.8

Interest cost
5.0

 
5.6

Amortization of prior service cost (credit)
(15.1
)
 
(16.2
)
Amortization of (gain) loss
(1.1
)
 
0.4

Net periodic benefit cost (income)
$
(10.0
)
 
$
(8.4
)