Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Jointly Owned Utility Plants

The following table summarizes our proportionate ownership interest in jointly-owned power plants:

As of December 31, 2018	Ownership Interest		Property, Plant & Equipment		Accumulated Depreciation			Construction in Progress
(in millions, except percentages)
Freestone Energy Center	75.0	%	$	379	$	(167	)	$	1
Hidalgo Energy Center	78.5	%	$	251	$	(114	)	$	4

Schedule of Components of Restricted Cash

The table below represents the components of our restricted cash as of December 31, 2018 and 2017 (in millions):

	2018						2017
	Current		Non-Current		Total		Current		Non-Current		Total
Debt service	$	13	$	8	$	21	$	11	$	8	$	19
Construction/major maintenance	23		24		47		28		16		44
Security/project/insurance	120		—		120		92		—		92
Other	11		2		13		3		1		4
Total	$	167	$	34	$	201	$	134	$	25	$	159

Schedule of Intangible Assets and Goodwill [Table Text Block]

As of December 31, 2018 and 2017, the components of our intangible assets were as follows (in millions):

	2018		2017		Lives
Acquired contracts	$	458	$	458	0 – 9 Years
Customer relationships	445		445		7 – 14 Years
Trademark and trade name	40		40		15 Years
Other	88		88		17 – 23 Years
	1,031		1,031
Less: Accumulated amortization	619		519
Intangible assets, net	$	412	$	512

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]

The estimated aggregate amortization expense of our intangible assets for the next five years is as follows (in millions):

2019	$	71
2020	$	44
2021	$	40
2022	$	35
2023	$	28

Schedule of Total Contractual Future Minimum Lease Receipts

The total contractual future minimum lease rentals for our contracts accounted for as operating leases at December 31, 2018, are as follows (in millions):

2019	$	342
2020	261
2021	257
2022	224
2023	141
Thereafter	239
Total	$	1,464

Future minimum rent payments under these lease agreements, including renewal options and rent escalation clauses, are as follows (in millions):

	Initial Year	2019		2020		2021		2022		2023		Thereafter		Total
Land and other operating leases	various	$	13	$	13	$	12	$	10	$	10	$	174	$	232
Power plant operating lease	2000	31		—		—		—		—		—		31
Total leases		$	44	$	13	$	12	$	10	$	10	$	174	$	263