Postretirement Benefit Obligations - Target Pension Plan Asset Allocation (Details)	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Total Pension Assets	100.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Pension Assets	2.00%
US and non-US equity securities
Defined Benefit Plan Disclosure [Line Items]
Total Pension Assets	65.00%
Fixed income / other securities
Defined Benefit Plan Disclosure [Line Items]
Total Pension Assets	33.00%