Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) from continuing operations	$ (744)	$ 1,185	$ 15	$ 2,267
Net income attributable to noncontrolling interests	7	12	14	22
Preferred stock dividends	55	55	118	118
Preferred stock discount accretion and redemptions	1	1	2	2
Net income (loss) from continuing operations attributable to common shareholders	(807)	1,117	(119)	2,125
Less: Dividends and undistributed earnings allocated to nonvested restricted shares	1	4	4	8
Net income (loss) from continuing operations attributable to basic common shareholders	(808)	1,113	(123)	2,117
Net income from discontinued operations attributable to common shareholders	4,399	189	4,555	378
Less: Undistributed earnings allocated to nonvested restricted shares	21	0	22	1
Net income from discontinued operations attributable to basic common shareholders	$ 4,378	$ 189	$ 4,533	$ 377
Basic weighted-average common shares outstanding (in shares)	426	451	428	453
Basic earnings (loss) per common share from continuing operations (in dollars per share)	$ (1.90)	$ 2.47	$ (0.29)	$ 4.68
Basic earnings per common share from discontinued operations (in dollars per share)	10.28	0.42	10.60	0.83
Basic earnings per common share (in dollars per share)	$ 8.40	$ 2.89	$ 10.33	$ 5.51
Less: Impact of earnings per share dilution from discontinued operations	$ 1	$ 2	$ 2	$ 5
Net income from discontinued operations attributable to diluted common shareholders	$ 4,377	$ 187	$ 4,531	$ 372
Dilutive potential common shares (in shares)	0	1	0	1
Diluted weighted-average common shares outstanding (in shares)	426	452	428	454
Diluted earnings (loss) per common share from continuing operations (in dollars per share)	$ (1.90)	$ 2.47	$ (0.29)	$ 4.67
Diluted earnings per common share from discontinued operations (in dollars per share)	10.28	0.41	10.59	0.82
Diluted earnings per common share (in dollars per share)	$ 8.40	$ 2.88	$ 10.32	$ 5.49