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Benefit Plans (Tables)
 3 Months Ended
Mar. 31, 2019
Retirement Benefits [Abstract]  
Components of Net Periodic Benefit Cost The components of net periodic benefit cost for defined benefit pension plans are summarized in the following table:
Three Months Ended March 31,
(Dollars in millions)
Location
2019
 
2018
Service cost
Personnel expense
$
54

 
$
60

Interest cost
Other expense
57

 
50

Estimated return on plan assets
Other expense
(113
)
 
(112
)
Amortization and other
Other expense
25

 
20

Net periodic benefit cost
 
$
23

 
$
18