Derivatives and Risk Management Activities - Net Unrealized Gain/(Loss) Recognized in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative assets and liabilities
Net loss reclassified to earnings	$ 3	$ 2	$ 8	$ 7
Net loss expected to be reclassified to earnings in the next twelve months			13
Other long-term assets, net
Derivative assets and liabilities
Interest rate fair value hedge liability at fair value	23		23
Other long-term liabilities and deferred credits
Derivative assets and liabilities
Interest rate fair value hedge liability at fair value	6		6
Other current liabilities
Derivative assets and liabilities
Interest rate fair value hedge liability at fair value					$ 44
AOCI cash flow hedge
Derivative assets and liabilities
Net loss deferred in AOCI	290		290
Interest Rate Derivatives
Derivative assets and liabilities
Net unrealized gain/(loss) recognized in AOCI	$ 22	$ (53)	$ (39)	$ (111)