Derivative and Hedging Activities - Fair Value Level 3 Measurements Table (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Assets (Liabilities), at Fair Value, Net, Period Start		$ 512
Derivative Assets (Liabilities), at Fair Value, Net, Period End	$ 512	(76)	$ 512
Commodity Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Assets (Liabilities), at Fair Value, Net, Period Start		267
Derivative Assets (Liabilities), at Fair Value, Net, Period End		(292)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Assets (Liabilities), at Fair Value, Net, Period End	206	209	206
Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Assets (Liabilities), at Fair Value, Net, Period Start		(91)	(54)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings		(8)	80
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements		28	(108)
Derivative Assets (Liabilities), at Fair Value, Net, Period End	(82)	(71)	(82)
Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member] | Oil, Natural Gas and NGL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings		(8)	80
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(20)	69
Fair Value, Inputs, Level 3 [Member] | Supply Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Assets (Liabilities), at Fair Value, Net, Period Start		297	1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings		13	220
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements		(30)	0
Derivative Assets (Liabilities), at Fair Value, Net, Period End	221	280	221
Fair Value, Inputs, Level 3 [Member] | Supply Contract [Member] | Marketing, Gathering And Compression [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ 220		(17)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ (17)	$ 220