Issuances of SEP Units - Effects of Issuances (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Noncontrolling Interest [Line Items]
Net Income—Controlling Interests	$ 195	$ 174	$ 578	$ 459
Increase in additional paid-in capital resulting from issuances of SEP units			457	330
Total net income—controlling interests and changes in equity—controlling interests	205	198	603	508
Additional Paid-in Capital
Noncontrolling Interest [Line Items]
Increase in additional paid-in capital resulting from issuances of SEP units	$ 10	$ 24	$ 25	$ 49