Guarantees and Indemnifications (Details) $ in Millions	Jun. 30, 2016 USD ($)
Guarantee Of Financial Obligations Of Npt [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$ 25.0
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2016 And 2018 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	35.8
Guarantee Of Rocky River Reality And Nusco Lease Payments For Real Estate And Vehicles Expiring 2019 Through 2024 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	10.1
Access Northeast Project Capital Contributions Guarantee Expiring In 2021 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	187.4
Guarantee Of Npt Letters Of Credit [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$ 14.0