Derivatives and Risk Management Activities - Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Derivative assets and liabilities
Asset Derivatives Fair Value	$ 96	$ 108
Liability Derivatives Fair Value	(183)	(481)
Net loss deferred in AOCI	219
Net loss expected to be reclassified to earnings in the next twelve months	8
Remaining loss expected to be reclassified to earnings through 2049	211
Derivatives in Hedging Relationships
Derivative assets and liabilities
Liability Derivatives Fair Value	(43)	(50)
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other current liabilities
Derivative assets and liabilities
Liability Derivatives Fair Value	(20)	(23)
Derivatives in Hedging Relationships | Interest Rate Derivatives | Other long-term liabilities and deferred credits
Derivative assets and liabilities
Liability Derivatives Fair Value	(23)	(27)
Derivatives Not Designated as a Hedge
Derivative assets and liabilities
Asset Derivatives Fair Value	96	108
Liability Derivatives Fair Value	(140)	(431)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other current assets
Derivative assets and liabilities
Asset Derivatives Fair Value	79	101
Liability Derivatives Fair Value	(81)	(344)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other long-term assets, net
Derivative assets and liabilities
Asset Derivatives Fair Value	13	2
Liability Derivatives Fair Value	(8)	(1)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other current liabilities
Derivative assets and liabilities
Asset Derivatives Fair Value	2
Liability Derivatives Fair Value	(7)	(14)
Derivatives Not Designated as a Hedge | Commodity Derivatives | Other long-term liabilities and deferred credits
Derivative assets and liabilities
Asset Derivatives Fair Value		2
Liability Derivatives Fair Value	(4)	(34)
Derivatives Not Designated as a Hedge | Foreign Currency Derivatives | Other current assets
Derivative assets and liabilities
Asset Derivatives Fair Value	1
Derivatives Not Designated as a Hedge | Foreign Currency Derivatives | Other current liabilities
Derivative assets and liabilities
Asset Derivatives Fair Value	1	3
Liability Derivatives Fair Value	(4)	(6)
Derivatives Not Designated as a Hedge | Preferred Distribution Rate Reset Option | Other long-term liabilities and deferred credits
Derivative assets and liabilities
Liability Derivatives Fair Value	$ (36)	$ (32)