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Retirement Benefits and Trusteed Assets (Tables)
 9 Months Ended
Sep. 30, 2017
Defined Benefit Plan [Abstract]  
Schedule of Net Periodic Benefit Costs (Credits)
The following tables detail the components of net periodic benefit costs (credits) for pension benefits and other postretirement benefits for DTE Energy:
 
Pension Benefits
 
Other Postretirement Benefits
 
2017
 
2016
 
2017
 
2016
Three Months Ended September 30,
(In millions)
Service cost
$
22

 
$
23

 
$
7

 
$
7

Interest cost
53

 
55

 
18

 
20

Expected return on plan assets
(78
)
 
(77
)
 
(33
)
 
(33
)
Amortization of:
 
 
 
 
 
 
 
Net actuarial loss
46

 
43

 
3

 
6

Prior service cost (credit)
1

 
—

 
(3
)
 
(29
)
Net periodic benefit cost (credit)
$
44

 
$
44

 
$
(8
)
 
$
(29
)
 
Pension Benefits
 
Other Postretirement Benefits
 
2017
 
2016
 
2017
 
2016
Nine Months Ended September 30,
(In millions)
Service cost
$
69

 
$
69

 
$
20

 
$
20

Interest cost
160

 
164

 
55

 
60

Expected return on plan assets
(233
)
 
(232
)
 
(98
)
 
(97
)
Amortization of:
 
 
 
 
 
 
 
Net actuarial loss
132

 
124

 
10

 
22

Prior service cost (credit)
1

 
—

 
(10
)
 
(88
)
Net periodic benefit cost (credit)
$
129

 
$
125

 
$
(23
)
 
$
(83
)
The following tables detail the components of net periodic benefit costs (credits) for pension benefits and other postretirement benefits for DTE Electric:
 
Pension Benefits
 
Other Postretirement Benefits
 
2017
 
2016
 
2017
 
2016
Three Months Ended September 30,
(In millions)
Service cost
$
16

 
$
18

 
$
5

 
$
5

Interest cost
40

 
42

 
14

 
15

Expected return on plan assets
(56
)
 
(55
)
 
(23
)
 
(23
)
Amortization of:
 
 
 
 
 
 
 
Net actuarial loss
32

 
31

 
2

 
4

Prior service cost (credit)
1

 
—

 
(2
)
 
(22
)
Net periodic benefit cost (credit)
$
33

 
$
36

 
$
(4
)
 
$
(21
)
 
Pension Benefits
 
Other Postretirement Benefits
 
2017
 
2016
 
2017
 
2016
Nine Months Ended September 30,
(In millions)
Service cost
$
53

 
$
53

 
$
15

 
$
15

Interest cost
121

 
125

 
42

 
46

Expected return on plan assets
(167
)
 
(165
)
 
(68
)
 
(68
)
Amortization of:
 
 
 
 
 
 
 
Net actuarial loss
94

 
88

 
6

 
15

Prior service cost (credit)
1

 
1

 
(7
)
 
(66
)
Net periodic benefit cost (credit)
$
102

 
$
102

 
$
(12
)
 
$
(58
)