Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) from continuing operations	$ 1,532	$ 1,181	$ 1,547	$ 3,448
Net income attributable to noncontrolling interests	13	13	27	35
Preferred stock dividends	63	63	181	181
Preferred stock discount accretion and redemptions	1	1	3	3
Net income from continuing operations attributable to common shareholders	1,455	1,104	1,336	3,229
Less: Dividends and undistributed earnings allocated to nonvested restricted shares	8	5	7	13
Net income from continuing operations attributable to basic common shareholders	1,447	1,099	1,329	3,216
Net income from discontinued operations attributable to common shareholders		211	4,555	589
Less: Undistributed earnings allocated to nonvested restricted shares		1	22	2
Net income from discontinued operations attributable to basic common shareholders		$ 210	$ 4,533	$ 587
Basic weighted-average common shares outstanding (in shares)	426	444	427	450
Basic earnings (loss) per common share from continuing operations (in dollars per share)	$ 3.40	$ 2.47	$ 3.11	$ 7.15
Basic earnings per common share from discontinued operations (in dollars per share)		0.48	10.61	1.30
Basic earnings per common share (in dollars per share)	$ 3.40	$ 2.95	$ 13.73	$ 8.45
Less: Impact of earnings per share dilution from discontinued operations		$ 2	$ 2	$ 7
Net income from discontinued operations attributable to diluted common shareholders		$ 208	$ 4,531	$ 580
Dilutive potential common shares (in shares)		1	1	1
Diluted weighted-average common shares outstanding (in shares)	426	445	428	451
Diluted earnings (loss) per common share from continuing operations (in dollars per share)	$ 3.39	$ 2.47	$ 3.11	$ 7.13
Diluted earnings per common share from discontinued operations (in dollars per share)		0.47	10.59	1.29
Diluted earnings per common share (in dollars per share)	$ 3.39	$ 2.94	$ 13.70	$ 8.42