Regulatory Assets and Liabilities Regulatory Assets and Liabilities - by Reportable Segment (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	$ 1,287	$ 1,514
Regulatory Liabilities	1,901	1,617
Brazil SBU
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	544	821
Regulatory Liabilities	1,059	798
US SBU
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	689	650
Regulatory Liabilities	842	819
MCAC SBU
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets	54	43
Regulatory Liabilities	$ 0	$ 0