Accounting for Derivative Instruments and Hedging Activities - Pre-tax effects of economic hedges not designated a cash flow hedges (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrealized mark-to-market results
Reversal of previously recognized unrealized (gains)/losses on settled positions related to economic hedges	$ (84)	$ (7)	$ (85)	$ 18
Reversal of acquired gain positions related to economic hedges	(10)	(2)	(11)	(1)
Net unrealized gains/(losses) on open positions related to economic hedges	25	(19)	158	(8)
Total unrealized mark-to-market (losses)/gains for economic hedging activities	(69)	(28)	62	9
Reversal of previously recognized unrealized gains on settled positions related to trading activity	(4)	(5)	(10)	(24)
Net unrealized gains on open positions related to trading activity	8	0	27	17
Total unrealized mark-to-market gains/(losses) for trading activity	4	(5)	17	(7)
Total unrealized (losses)/gains	(65)	(33)	79	2
Credit Risk Related Contingent Features
Unrealized gain (loss) from open economic hedge positions			158	(8)
Collateral due on net liability position that has not been called by a certain marginable agreement counterparty	6		6
Adequate Assurance Clauses
Credit Risk Related Contingent Features
Derivative net liability position, collateral required Contracts with Credit Rating Contingent Feature	25		25
Credit Rating Contingent Features
Credit Risk Related Contingent Features
Derivative net liability position, collateral required Contracts with Credit Rating Contingent Feature	17		17
Commodity contracts
Unrealized mark-to-market results
Total unrealized (losses)/gains	(65)	(33)	79	2
Commodity contracts \| Operating revenues
Unrealized mark-to-market results
Total unrealized (losses)/gains	59	17	(14)	170
Commodity contracts \| Cost of operations
Unrealized mark-to-market results
Total unrealized (losses)/gains	(124)	(50)	93	(168)
Interest rate contracts
Unrealized mark-to-market results
Total unrealized (losses)/gains	$ 2	$ 3	$ 17	$ (4)

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This element represents the amount recorded in the entity's statement of operations for net unrealized gains (losses) on open positions related to trading activities.

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No definition available.

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Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to acquired economic hedges.

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Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to economic hedges.

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Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to trading activities.

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- Definition

Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities

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Unrealized Gain (Loss) on Derivatives, Mark To Market, Trading Activities

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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