Benefit Plans (Estimated Net Loss and Prior Service Cost (Credit) Expected to be Amortized in 2017) (Details) $ in Millions |
Dec. 31, 2017
USD ($)
|
---|---|
Pension [Member] | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |
Estimated future net loss | $ 228 |
Estimated future prior service cost (credit) | 4 |
Postretirement Benefit Plan [Member] | |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | |
Estimated future net loss | 35 |
Estimated future prior service cost (credit) | $ (42) |