Postretirement Plans Postretirement Plans Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 3,500
Cash Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	500
Defined Benefit Plan, Plan Assets, Contributions by Employer	500
Non-Cash Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 3,500