Derivative Instruments and Hedging Activities (Assets and Liabilities - Current vs. Noncurrent Derivative instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative Asset, Current	$ 77	$ 32
Derivative Liability, Current	148	157
Derivative Asset, Noncurrent	203	208
Derivative Liability, Noncurrent	366	214
Total asset derivatives	280	240
Total liability derivatives	514	371
Asset, Formerly Accounted for as a Derivative, to be Amortized into Earnings	161	169
Liability, Formerly Accounted for as a Derivative, to be Amortized into Earnings	180	190
Contracts Subject To Netting Arrangements
Derivatives, Fair Value [Line Items]
Total asset derivatives	53	91
Total liability derivatives	507	314
Derivative Assets Not Offset Under Netting Arrangements	(10)	(9)
Derivative Liabilities Not Offset Under Netting Arrangements	(10)	(9)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	(3)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(5)	(6)
Derivative Asset	43	79
Derivative Liability	$ 492	$ 299