| **Benefit Plans (Schedule of estimated amounts to be recognized from Accumulated other comprehensive income into net periodic cost (benefit) during next fiscal year) (Details) $ in Millions** | Dec. 31, 2017 USD ($) |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|
| Pension Plans, Defined Benefit                                                                                                                                                                  |                  |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                                                                |                  |
| Amortization of prior service credit                                                                                                                                                            | $ 0                   |
| Amortization of net actuarial loss                                                                                                                                                              | 36                    |
| Total estimated amounts to be recognized                                                                                                                                                        | 36                    |
| Other Postretirement Benefits Plan                                                                                                                                                              |                  |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                                                                |                  |
| Amortization of prior service credit                                                                                                                                                            | (2)                   |
| Amortization of net actuarial loss                                                                                                                                                              | 0                     |
| Total estimated amounts to be recognized                                                                                                                                                        | $ (2)                 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of cost (credit) included in accumulated other comprehensive (income) loss expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (s) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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