Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income (loss) from continuing operations	$ 1,103	$ (744)	$ 2,929	$ 15
Net income attributable to noncontrolling interests	12	7	22	14
Preferred stock dividends	48	55	105	118
Preferred stock discount accretion and redemptions	1	1	2	2
Net income (loss) from continuing operations attributable to common shareholders	1,042	(807)	2,800	(119)
Less: Dividends and undistributed earnings allocated to nonvested restricted shares	5	1	13	4
Net income (loss) from continuing operations attributable to basic common shareholders	$ 1,037	(808)	$ 2,787	(123)
Net income from discontinued operations attributable to common shareholders		4,399		4,555
Less: Undistributed earnings allocated to nonvested restricted shares		21		22
Net income from discontinued operations attributable to basic common shareholders		$ 4,378		$ 4,533
Basic weighted-average common shares outstanding (in shares)	427	426	426	428
Basic earnings (loss) per common share from continuing operations (in dollars per share)	$ 2.43	$ (1.90)	$ 6.54	$ (0.29)
Basic earnings per common share from discontinued operations (in dollars per share)		10.28		10.60
Basic earnings per common share (in dollars per share)	$ 2.43	$ 8.40	$ 6.54	$ 10.33
Net income (loss) from continuing operations attributable to diluted common shareholders	$ 1,037	$ (808)	$ 2,787	$ (123)
Less: Impact of earnings per share dilution from discontinued operations		1		2
Net income from discontinued operations attributable to diluted common shareholders		$ 4,377		$ 4,531
Dilutive potential common shares (in shares)			1
Diluted weighted-average common shares outstanding (in shares)	427	426	427	428
Diluted earnings (loss) per common share from continuing operations (in dollars per share)	$ 2.43	$ (1.90)	$ 6.53	$ (0.29)
Diluted earnings per common share from discontinued operations (in dollars per share)		10.28		10.59
Diluted earnings per common share (in dollars per share)	$ 2.43	$ 8.40	$ 6.53	$ 10.32