Fair Value of FInancial Instruments Fair Value Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized and unrealized losses	$ 10	$ (40)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0
Net transfers out of Level 3 to Level 2	(1)	(11)
Net liabilities from price risk management activities as of end of year	97	88	$ 139
Level 3 net unrealized losses that have been fully offset by the effect of regulatory accounting	16	(32)
Net realized losses	$ (6)	$ (8)