Risk Management Activities and Fair Value Measurements Risk Management Activities and Fair Value Measurements - Additional Information (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long Term Debt, Current Maturities measured at Fair Value	$ 4,312	$ 4,400