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Benefits (Tables)
 3 Months Ended
Mar. 31, 2014
Benefits (Tables) [Abstract]  
Components of net periodic pension and OPEB costs
 
 
Pension Costs
 
OPEB Costs
Benefit Plan Cost Components
 
2014
 
2013
 
2014
 
2013
 
 
(Millions of Dollars)
Net Periodic Benefit Cost
 
 
 
 
 
 
 
 
Service cost
 
$
2.7

 
$
4.2

 
$
2.2

 
$
2.7

Interest cost
 
17.1

 
15.1

 
4.5

 
3.9

Expected return on plan assets
 
(24.7
)
 
(24.0
)
 
(5.9
)
 
(5.3
)
Amortization of:
 
 
 
 
 
 
 
 
Prior service cost (credit)
 
0.5

 
0.6

 
(0.5
)
 
(0.5
)
Actuarial loss
 
9.1

 
13.6

 
0.2

 
0.9

Net Periodic Benefit Cost
 
$
4.7

 
$
9.5

 
$
0.5

 
$
1.7