Risk Management Effect of Derivative Contracts on the Income Statement (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (39)	$ (10)	$ 7	$ (10)
Derivative, Loss on Derivative	7		2
Energy Related Derivative [Member] | Natural Gas Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(2)	(9)	3	(16)
Energy Related Derivative [Member] | Revenues - Product sales and other [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(40)	2	4	1
Energy Related Derivative [Member] | Gas purchases and other costs of sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	3	(3)	0	7
Energy Related Derivative [Member] | Other Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0	0	0	(2)
Designated as Hedging Instrument [Member] | Operating Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	57	(16)	129	(30)
Amount of gain/(loss)recognized in incomeon derivative(ineffective portionand amountexcluded fromeffectiveness testing)	3	(27)	10	(32)
Designated as Hedging Instrument [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)recognized in OCI on derivative(effective portion)	(58)	(96)	(60)	(141)
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Interest expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	(233)	57	(88)	112
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Interest expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	0	(2)	(1)	(2)
Amount of gain/(loss)recognized in incomeon derivative(ineffective portionand amountexcluded fromeffectiveness testing)	0	0	0	0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)recognized in OCI on derivative(effective portion)	1	(8)	(2)	(10)
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Interest expense [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	256	(57)	117	(112)
Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss to be reclassified within twelve months			182
Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Natural Gas Revenue [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	1	0	25	(9)
Amount of gain/(loss)recognized in incomeon derivative(ineffective portionand amountexcluded fromeffectiveness testing)	0	0	0	0
Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Revenues - Product sales and other [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	37	(19)	101	(25)
Amount of gain/(loss)recognized in incomeon derivative(ineffective portionand amountexcluded fromeffectiveness testing)	3	(27)	10	(32)
Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Gas purchases and other costs of sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	(14)	5	(19)	6
Amount of gain/(loss)recognized in incomeon derivative(ineffective portionand amountexcluded fromeffectiveness testing)	0	0	0	0
Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)recognized in OCI on derivative(effective portion)	(82)	(88)	(47)	(131)
Designated as Hedging Instrument [Member] | Currency Swap [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)recognized in OCI on derivative(effective portion)	23	0	(11)	0
Designated as Hedging Instrument [Member] | Other Credit Derivatives [Member] | Other Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss)reclassified fromAccumulated OCIinto income(effective portion)	$ 33	$ 0	$ 23	$ 0