Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Summary of Significant Accounting Policies Disclosure
Finite-Lived Intangible Assets, Accumulated Amortization	$ 1,775,000,000	$ 1,525,000,000	[1]
Allowance for Doubtful Accounts Receivable, Current	30,000,000	21,000,000
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount	46,000,000	29,000,000		$ 19,000,000	$ 2,000,000
Redeemable Noncontrolling Interest, Distributions from Noncontrolling Interests	(1,000,000)
Redeemable Noncontrolling Interest, Cash Contributions from Noncontrolling Interest Holders	$ 56,000,000	27,000,000		36,000,000
Inventory Write-down		19,000,000
Funds Deposited by Counterparties
Number of months beyond which company can not predict the holding of collateral (in months)	12 months
Project Development Costs and Capitalized Interest
Amount of interest capitalized	$ 43,000,000	30,000,000		29,000,000
Income Taxes
Unrecognized tax benefits, more-likely-than-not threshold percentage	50.00%
Revenue Recognition
Energy revenues from resales of purchased power	$ 154,000,000	165,000,000		387,000,000
Unbilled revenues	321,000,000	309,000,000		341,000,000
Leases [Abstract]
Operating Leases, Income Statement, Contingent Revenue	936,000,000	777,000,000		544,000,000
Gross Receipts and Sales Taxes
Gross Receipts Tax	102,000,000	110,000,000		108,000,000
Cost of Energy for Retail Operations
Transmission and distribution charges not yet billed	90,000,000	85,000,000		86,000,000
Foreign Currency Translation and Transaction Gains and Losses
Cumulative translation adjustment	(11,000,000)	(10,000,000)		1,000,000
Tax Equity Arrangements [Abstract]
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(38,000,000)	(17,000,000)		(19,000,000)
Marketing and Advertising Expense
Marketing and advertising expense	247,000,000	307,000,000		208,000,000
Advertising Expense	53,000,000	$ 135,000,000		$ 87,000,000
Indefinite-Lived Intangible Assets (Excluding Goodwill)	$ 0
South Texas Project
Property, Plant and Equipment
Ownership Interest (as a percent)	44.00%
Current Debt Service Payment [Member]
Summary of Significant Accounting Policies Disclosure
Restricted Cash and Cash Equivalents	$ 53,000,000
Operating Expense [Member]
Summary of Significant Accounting Policies Disclosure
Restricted Cash and Cash Equivalents	51,000,000
Distributions [Member]
Summary of Significant Accounting Policies Disclosure
Restricted Cash and Cash Equivalents	58,000,000
Reserves [Member]
Summary of Significant Accounting Policies Disclosure
Restricted Cash and Cash Equivalents	$ 284,000,000

[1] Adjusted for write-off of fully amortized emission allowances of $154 million.