Earnings per Share (Unaudited) Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net (loss) income from continuing operations	$ (74)	$ 1,039	$ 1	$ 1,867
Net loss (income) from continuing operations attributable to noncontrolling interests	2	(166)	(43)	(291)
Undistributed earnings allocated to participating securities	(3)	(3)	(3)	(4)
Net (loss) income from continuing operations attributable to common stockholders	(75)	870	(45)	1,572
Net (loss) income from discontinued operations attributable to common stockholders	0	(4)	1	(15)
Net (loss) income attributable to common stockholders	$ (75)	$ 866	$ (44)	$ 1,557
Basic weighted-average shares of common stock outstanding	1,451	1,449	1,451	1,449
Add shares issuable upon exercise or vesting of dilutive stock options and restricted stock unitsa	0	9	0	9
Diluted weighted-average shares of common stock outstanding	1,451	1,458	1,451	1,458
Basic net (loss) income per share attributable to common stockholders:
Continuing operations (in dollars per share)	$ (0.05)	$ 0.60	$ (0.03)	$ 1.08
Discontinued operations (in dollars per share)	0	0	0	(0.01)
Earnings per share, basic (in dollars per share)	(0.05)	0.60	(0.03)	1.07
Diluted net (loss) income per share attributable to common stockholders:
Continuing operations (in dollars per share)	(0.05)	0.59	(0.03)	1.08
Discontinued operations (in dollars per share)	0	0	0	(0.01)
Earnings per share, diluted (in dollars per share)	$ (0.05)	$ 0.59	$ (0.03)	$ 1.07
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	10	2	12	3
Dilutive Securities Excluded from Computation of EPS Amount	43	35	41	34