Accounting for Derivative Instruments and Hedging Activities - Pre-tax Effects of Economic Hedges not Designated as Cash Flow Hedges (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrealized Mark To Market Results [Abstract]
Reversal of previously recognized unrealized (gains) on settled positions related to economic hedges	$ (55)	$ (68)	$ (73)
Reversal of acquired loss/(gain) positions related to economic hedges	4	6	(10)
Net unrealized (losses)/gains on open positions related to economic hedges	68	(42)	(97)
Total unrealized mark-to-market (losses)/gains for economic hedging activities	(119)	(20)	14
Reversal of previously recognized unrealized (gains) on settled positions related to trading activity	(20)	(11)	(12)
Net unrealized gains on open positions related to trading activity	15	31	29
Total unrealized mark-to-market (losses)/gains for trading activity	(5)	20	17
Total unrealized (losses)/gains	(124)	0	31
Credit Risk Related Contingent Features [Abstract]
Collateral required contracts with credit rating contingent features in a net liability position	35
Additional collateral required	1
Adequate Assurance Clauses
Credit Risk Related Contingent Features [Abstract]
Collateral required for contracts in net liability positions that have adequate assurance clauses	26
Commodity contracts
Unrealized Mark To Market Results [Abstract]
Total unrealized (losses)/gains	(124)	0	31
Commodity contracts \| Operating revenue
Unrealized Mark To Market Results [Abstract]
Total unrealized (losses)/gains	90	53	(113)
Commodity contracts \| Cost of operations
Unrealized Mark To Market Results [Abstract]
Total unrealized (losses)/gains	(214)	(53)	144
Interest rate contracts
Unrealized Mark To Market Results [Abstract]
Total unrealized (losses)/gains	$ 0	$ (38)	$ 0

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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.

+ References

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 economic hedges.

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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 trading activities.

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No definition available.

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- Definition

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

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No definition available.

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

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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-Publisher FASB
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-Section 50
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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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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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