Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	12	8	12
Income (loss) from operations	$ 96	$ (153)	$ 452	$ (203)
Discontinued operations	0	14	0	(4,893)
Net income (loss)	$ 96	$ (139)	$ 452	$ (5,096)
Weighted average common shares outstanding, basic	854	850	853	850
Effect of dilutive securities	1	0	1	0
Weighted average common shares, diluted	855	850	854	850
Basic:
Income (loss) from continuing operations, per basic share	$ 0.11	$ (0.18)	$ 0.53	$ (0.24)
Income (loss) from discontinued operations, per basic share	0.00	0.02	0.00	(5.76)
Net income (loss), per basic share	0.11	(0.16)	0.53	(6.00)
Diluted:
Income (loss) from continuing operations, per diluted share	0.11	(0.18)	0.53	(0.24)
Income (loss) from discontinued operations, per diluted share	0.00	0.02	0.00	(5.76)
Net income (loss), per diluted share	$ 0.11	$ (0.16)	$ 0.53	$ (6.00)