Employee Benefits - Cash Flows (Details) $ in Millions	Dec. 31, 2015 USD ($)
Retirement Plans [Member]
Information about the expected cash flows for retirement and post-retirement plans and impact of the Medicare subsidy
2016, Net payments	$ 91
2017, Net payments	90
2018, Net payments	93
2019, Net payments	96
2020, Net payments	99
2021-2025, Net payments	539
Postretirement Plans [Member]
Information about the expected cash flows for retirement and post-retirement plans and impact of the Medicare subsidy
2016, Gross payments	13
2017, Gross payments	13
2018, Gross payments	12
2019, Gross payments	12
2020, Gross payments	11
2021-2025, Gross payments	43
2016, Retiree Contributions	(4)
2017, Retiree Contributions	(4)
2018, Retiree Contributions	(4)
2019, Retiree Contributions	(4)
2020, Retiree Contributions	(4)
2021-2025, Retiree Contributions	(12)
2016, Medicare subsidy	(1)
2017, Medicare subsidy	(1)
2018, Medicare subsidy	(1)
2019, Medicare subsidy	(1)
2020, Medicare subsidy	(1)
2021-2025, Medicare subsidy	(3)
2016, Net payments	8
2017, Net payments	8
2018, Net payments	7
2019, Net payments	7
2020, Net payments	6
2021-2025, Net payments	$ 28

Defined benefit plan expected future benefit payments gross in five fiscal years thereafter.

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Defined benefit plan expected future benefit payments gross in year five.

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Defined benefit plan expected future benefit payments gross in year four.

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Defined benefit plan expected future benefit payments gross in year one.

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- Definition

Defined benefit plan expected future benefit payments gross in year three.

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Defined benefit plan expected future benefit payments gross in year two.

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- Definition

Defined benefit plan expected future benefit payments retiree contributions in five fiscal years thereafter.

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Defined benefit plan expected future benefit payments retiree contributions in year five.

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Defined benefit plan expected future benefit payments retiree contributions in year four.

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Defined benefit plan expected future benefit payments retiree contributions in year one.

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Defined benefit plan expected future benefit payments retiree contributions in year three.

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Defined benefit plan expected future benefit payments retiree contributions in year two.

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Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of the prescription drug subsidy receipts to be received after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

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Amount of the prescription drug subsidy receipts to be received in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of the prescription drug subsidy receipts to be received in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of the prescription drug subsidy receipts to be received in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of the prescription drug subsidy receipts to be received in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of the prescription drug subsidy receipts to be received in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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