Investing Activities Summarized Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity Method Investment, Summarized Financial Information [Abstract]
Gross revenue	$ 226	$ 241	$ 648	$ 658
Operating income	132	131	376	334
Net income	$ 117	$ 113	$ 321	$ 281