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Retirement Plan and Postretirement Benefits Retirement Plan and Postretirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]  
Schedule of Net Benefit Costs [Table Text Block]
Net periodic benefit cost for the plans included the following components for the years ended December 31 (in millions):
 
Pension
 
Other Postretirement
 
2018
 
2017
 
2016
 
2018
 
2017
 
2016
 
 
 
 
 
 
 
 
 
 
 
 
Service cost
$
21

 
$
24

 
$
29

 
$
9

 
$
9

 
$
9

Interest cost
105

 
116

 
126

 
24

 
29

 
31

Expected return on plan assets
(164
)
 
(160
)
 
(160
)
 
(41
)
 
(40
)
 
(41
)
Settlement
21

 
—

 
—

 
—

 
—

 
—

Net amortization
28

 
25

 
46

 
(13
)
 
(14
)
 
(12
)
Net periodic benefit cost (credit)
$
11

 
$
5

 
$
41

 
$
(21
)
 
$
(16
)
 
$
(13
)

Net periodic benefit cost for the UK Plan included the following components for the years ended December 31 (in millions):
 
2018
 
2017
 
2016
 
 
 
 
 
 
Service cost
$
19

 
$
23

 
$
20

Interest cost
56

 
58

 
72

Expected return on plan assets
(101
)
 
(100
)
 
(110
)
Settlement
44

 
31

 
—

Net amortization
45

 
63

 
44

Net periodic benefit cost
$
63

 
$
75

 
$
26

    
Nevada Power Company [Member]  
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]  
Schedule of Amounts Recognized in Balance Sheet [Table Text Block]
Amounts receivable from (payable to) NV Energy are included on the Consolidated Balance Sheets and consist of the following as of December 31 (in millions):
 
2018
 
2017
Qualified Pension Plan -
 
 
 
Other long-term liabilities
$
(26
)
 
$
(23
)
 
 
 
 
Non-Qualified Pension Plans:
 
 
 
Other current liabilities
(1
)
 
(1
)
Other long-term liabilities
(9
)
 
(10
)
 
 
 
 
Other Postretirement Plans -
 
 
 
Other long-term liabilities
(1
)
 
1
Sierra Pacific Power Company [Member]  
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]  
Schedule of Amounts Recognized in Balance Sheet [Table Text Block]
Amounts payable to NV Energy are included on the Balance Sheets and consist of the following as of December 31(in millions):
 
2018
 
2017
Qualified Pension Plan -
 
 
 
Other long-term liabilities
$
(19
)
 
$
(2
)
 
 
 
 
Non-Qualified Pension Plans:
 
 
 
Other current liabilities
(1
)
 
(1
)
Other long-term liabilities
(7
)
 
(8
)
 
 
 
 
Other Postretirement Plans -
 
 
 
Other long-term liabilities
(13
)
 
(20
)