Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	10	13	11	13
Income (loss) from operations	$ (599)	$ (206)	$ (802)	$ (704)
Discontinued operations	0	14	(4,893)	(65)
Net income (loss)	$ (599)	$ (192)	$ (5,695)	$ (769)
Weighted average common shares outstanding, basic	850	847	850	809
Basic:
Income (loss) from continuing operations, per basic share	$ (0.70)	$ (0.24)	$ (0.94)	$ (0.87)
Income (loss) from discontinued operations, per basic share	0.00	0.01	(5.76)	(0.08)
Net income (loss), per basic share	(0.70)	(0.23)	(6.70)	(0.95)
Diluted:
Income (loss) from continuing operations, per diluted share	(0.70)	(0.24)	(0.94)	(0.87)
Income (loss) from discontinued operations, per diluted share	0.00	0.01	(5.76)	(0.08)
Net income (loss), per diluted share	$ (0.70)	$ (0.23)	$ (6.70)	$ (0.95)