Leases Maturity of Operating Lease Liability (Details) $ in Millions	Dec. 31, 2018 USD ($)
Assets subject to contracts accounted for as operating leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 50	[1]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	40	[2]
Operating Leases, Future Minimum Payments, Due in Two Years	19	[1]
Capital Leases, Future Minimum Payments Due in Two Years	40	[2]
Operating Leases, Future Minimum Payments, Due in Three Years	20	[1]
Capital Leases, Future Minimum Payments Due in Three Years	38	[2]
Operating Leases, Future Minimum Payments, Due in Four Years	18	[1]
Capital Leases, Future Minimum Payments Due in Four Years	33	[2]
Operating Leases, Future Minimum Payments, Due in Five Years	17	[1]
Capital Leases, Future Minimum Payments Due in Five Years	27	[2]
Operating Leases, Future Minimum Payments, Due Thereafter	192	[1]
Capital Leases, Future Minimum Payments Due Thereafter	92	[2]
Operating Leases, Future Minimum Payments Due	316	[1]
Capital Leases, Future Minimum Payments Due	270	[2]
Capital Leases, Future Minimum Payments, Interest Included in Payments	89	[2]
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	$ 181	[2]

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

[2] Includes a failed sale-leaseback transaction related to our Pasadena Power Plant.