Commitments and Contingencies (Schedules of Future Minimum Rental Payments) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	[1]		$ 50
Operating Leases, Future Minimum Payments, Due in Two Years	[1]		19
Operating Leases, Future Minimum Payments, Due in Three Years	[1]		20
Operating Leases, Future Minimum Payments, Due in Four Years	[1]		18
Operating Leases, Future Minimum Payments, Due in Five Years	[1]		17
Operating Leases, Future Minimum Payments, Due Thereafter	[1]		192
Operating Leases, Future Minimum Payments Due	[1]		$ 316
Natural Gas [Member]
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 402
Operating Leases, Future Minimum Payments, Due in Two Years		178
Operating Leases, Future Minimum Payments, Due in Three Years		121
Operating Leases, Future Minimum Payments, Due in Four Years		98
Operating Leases, Future Minimum Payments, Due in Five Years		41
Operating Leases, Future Minimum Payments, Due Thereafter		103
Operating Leases, Future Minimum Payments Due		$ 943

[1] During the years ended December 31, 2018 and 2017, expense for operating leases amounted to $53 million and $50 million, respectively.