Risk Management and Hedging Activities - Information about Interest Rate Swaps (Details) - Interest rate swaps - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Gross Amounts Presented in the Condensed Consolidated Balance Sheets, Assets	$ 56	$ 37
Amounts Not Offset in the Condensed Consolidated Balance Sheets, Assets	0	0
Net Amount	$ 56	$ 37