Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues	$ 457	$ 421	$ 418	$ 403	$ 432	$ 422	$ 408	$ 383	$ 1,699	$ 1,645	$ 1,682
Less: Net income attributable to noncontrolling interests in subsidiaries									0	1	1
Operating Income (Loss)	58	60	5	(14)	43	74	(15)	7	109	109	154
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	8	54	(29)	(37)	78	34	(6)	(37)	(4)	69	(1)
Net Income (Loss) Attributable to Parent	$ 8	$ 54	$ (29)	$ (37)	$ 77	$ 34	$ (6)	$ (37)	$ (4)	$ 68	$ (2)
Earnings Per Share, Basic	$ 0.06	$ 0.42	$ (0.23)	$ (0.29)	$ 0.59	$ 0.26	$ (0.05)	$ (0.28)	$ (0.03)	$ 0.52	$ (0.01)
Earnings Per Share, Diluted	0.06	0.42	(0.23)	(0.29)	0.58	0.25	(0.05)	(0.28)	(0.03)	0.51	(0.01)
Common Stock, Dividends, Per Share, Declared	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1.00	$ 1.00	$ 0.86
Net Interest Expense On Project Debt					$ (1)	$ 3	$ 5	$ 2		$ 9	$ 10