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Pension, Savings, And Other Employee Benefits (Schedule of Assumptions Used in the Defined Benefit Plans) (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Qualified pension |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate |  |  |  | 3.76% | 4.39% | 4.68%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate |  |  |  | 4.37% | 4.69% | 4.30%
Nonqualified pension |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate |  |  |  | 3.59% | 4.07% | 4.33%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate |  |  |  | 4.07% | 4.34% | 4.00%
Other nonqualified pension |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate |  |  |  | 3.19% | 3.39% | 3.57%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate |  |  |  | 3.39% | 3.57% | 3.35%
Postretirement benefits | Minimum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate |  |  |  | 3.37% | 3.67% | 3.76%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.68% | 3.84% | 3.45% |  |  |
Postretirement benefits | Maximum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate |  |  |  | 3.87% | 4.57% | 4.87%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 4.57% | 4.87% | 4.45% |  |  |
Qualified pension/ postretirement benefits |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation expected long term return on assets |  |  |  | 4.20% | 4.50% | 6.00%
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets |  |  |  | 4.50% | 6.00% | 5.85%
Postretirement benefit (retirees post January 1, 1993) |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation expected long term return on assets |  |  |  | 5.95% | 6.00% | 6.15%
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets |  |  |  | 6.00% | 6.15% | 6.35%
Postretirement benefit (retirees prior to January 1, 1993) |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation expected long term return on assets |  |  |  | 2.15% | 2.15% | 2.10%
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets |  |  |  | 2.15% | 2.10% | 2.30%

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- Definition Defined Benefit Plan Assumptions Used In Calculating Benefit Obligation Expected Long Term Return On Assets + References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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