Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Common 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
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income (loss) from continuing operations, net of tax	$ 3,537	$ (917)	$ 6,864	$ (2,257)
Loss from discontinued operations, net of tax	(1)	(1)	(3)	(1)
Net income (loss)	3,536	(918)	6,861	(2,258)
Dividends and undistributed earnings allocated to participating securities	(30)	(1)	(58)	(4)
Preferred stock dividends	(60)	(90)	(121)	(145)
Issuance cost for redeemed preferred stock	0	0	0	(22)
Net income (loss) available to common stockholders	$ 3,446	$ (1,009)	$ 6,682	$ (2,429)
Total weighted-average basic common shares outstanding	450.6	456.7	454.6	457.1
Effect of dilutive securities:
Stock options	0.8	0.0	0.8	0.0
Other contingently issuable shares	0.9	0.0	0.8	0.0
Total effect of dilutive securities	1.7	0.0	1.6	0.0
Total weighted-average diluted common shares outstanding	452.3	456.7	456.2	457.1
Basic earnings per common share:
Net income (loss) from continuing operations (in dollars per share)	$ 7.65	$ (2.21)	$ 14.70	$ (5.31)
Net income (loss) per basic common share (in dollars per share)	7.65	(2.21)	14.70	(5.31)
Diluted earnings per common share:
Net income (loss) from continuing operations (in dollars per share)	7.62	(2.21)	14.65	(5.31)
Net income (loss) per diluted common share (in dollars per share)	$ 7.62	$ (2.21)	$ 14.65	$ (5.31)