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Pension, Savings, and Other Employee Benefits - Schedule of Assumptions Used in the Defined Benefit Plans (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Minimum required outstanding par value to each issue of bonds | $ 300,000,000 | $ 300,000,000 | $ 250,000,000
Qualified pension |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate | 4.43% | 3.76% | 4.39%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.75% | 4.37% | 4.69%
Nonqualified pension |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate | 4.26% | 3.59% | 4.07%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.59% | 4.07% | 4.34%
Other nonqualified pension |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate | 3.83% | 3.19% | 3.39%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.19% | 3.39% | 3.57%
Postretirement benefits | Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate | 4.03% | 3.37% | 3.67%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.35% | 3.68% | 3.84%
Postretirement benefits | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan assumptions used calculating benefit obligation, discount rate | 4.56% | 3.87% | 4.57%
Defined benefit plan assumptions used calculating net periodic benefit cost, discount rate | 3.87% | 4.57% | 4.87%
Qualified pension/ postretirement benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Expected time horizon | 30 years |  |
Defined benefit plan assumptions used calculating benefit obligation expected long term return on assets | 4.20% |  |
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets | 4.20% | 4.50% | 6.00%
Qualified pension/ postretirement benefits | Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Term used for assumption calculation | 6 months |  |
Qualified pension/ postretirement benefits | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Term used for assumption calculation | 30 years |  |
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% |  |
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets | 5.95% | 6.00% | 6.15%
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% |  |
Defined benefit plan assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets | 2.15% | 2.15% | 2.10%

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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 Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Return Time Horizon + References No definition available. + Details
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- Definition Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Assumptions Term + References No definition available. + Details
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- Definition Minimum amount of outstanding par value to each issue of bonds selected to create hypothetical yield curve. + 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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