Regulatory Assets and Liabilities Regulatory Assets and Liabilities - by Reportable Segment (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 1,664	$ 1,509
Regulatory Liabilities	1,751	2,114	$ 269
Brazil SBU
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	971	787
Regulatory Liabilities	932	1,347
US SBU
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	650	631
Regulatory Liabilities	819	767
MCAC SBU (El Salvador)
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	43	91
Regulatory Liabilities	$ 0	$ 0