Derivative Financial Instruments - Hedging of Debt Portfolio (Details) - 3 months ended Sep. 30, 2017 € in Millions, £ in Millions, gal in Millions, $ in Millions	GBP (£) gal	EUR (€)	USD ($)
Interest rate swap February 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value			$ 500
Interest rate swap, April 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value			500
Interest rate swap October 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value			750
Interest rate swap July 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value			$ 500
Hedging of foreign currency risk, July 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | £	£ 234
Hedging of foreign currency risk, August 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | €		€ 534
Hedging of foreign currency risk, June 2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | €		€ 500
Fuel swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount (in gallons) | gal	49