Retirement Benefits (Details 7)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Assumptions Used to Determine Benefit Obligation
Discount rate	4.19%	4.53%
Initial cash balance crediting rate assumed for the next year	3.10%	3.00%
Rate to which the cash balance crediting rate is assumed to increase (the ultimate rate)	3.60%	3.75%
Year that the cash balance crediting rate reaches the ultimate rate	2022	2021
Rate of compensation increase	3.00%	3.00%
Assumptions Used to Determine Benefit Cost
Discount rate	4.53%	4.12%
Initial cash balance crediting rate assumed for the next year	3.00%	2.75%
Rate to which the cash balance crediting rate is assumed to increase (the ultimate rate)	3.75%	3.50%
Year that the cash balance crediting rate reaches the ultimate rate	2021	2020
Expected long-term return on plan assets	8.00%	8.00%
Rate of compensation increase	3.00%	3.00%
Medical and Life Benefits
Assumptions Used to Determine Benefit Obligation
Discount rate	4.13%	4.47%
Assumptions Used to Determine Benefit Cost
Discount rate	4.47%	4.04%
Expected long-term return on plan assets	7.70%	7.58%
Benefit Obligation [Member]
Defined Benefit Plan Disclosure (Table Amounts)
Initial health care cost trend rate assumed for the next year	6.50%	7.00%
Rate to which the health care cost trend rate is assumed to decline (the ultimate trend rate)	5.00%	5.00%
Year that the health care cost trend rate reaches the ultimate trend rate	2020	2020
Post-retirement Benefit Cost
Defined Benefit Plan Disclosure (Table Amounts)
Initial health care cost trend rate assumed for the next year	7.00%	6.50%
Rate to which the health care cost trend rate is assumed to decline (the ultimate trend rate)	5.00%	5.00%
Year that the health care cost trend rate reaches the ultimate trend rate	2020	2019

Cash Balance Crediting Rate Assumed for next fiscal year used to calculate benefit cost

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Defined Benefit Plan, Cash Balance Crediting Rate, Year that the rate reaches the ultimate rate, used to calculate benefit cost.

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Defined Benefit Plan Ultimate Cash Balance Crediting Rate, used to calculate benefit cost

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Cash Balance Crediting Rate Assumed for Next Fiscal Year used to calculate the benefit obligation.

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Defined Benefit Plan, Cash Balance Crediting Rate, Year that rate reaches ultimate rate, used to calculate benefit obligation, in CCYY format.

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Defined Benefit Plan Ultimate Cash Balance Crediting Rate used to calculate the benefit obligation

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The interest rate used to adjust for the time value of money for the plan.

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Expected rate of compensation increases (for pay-related plans).

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The interest rate used to adjust for the time value of money.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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Expected rate of compensation increases (for pay-related plans).

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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.

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The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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The ultimate trend rate for health care costs.

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Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

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