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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Income from continuing operations, net of tax	$ 3,104	$ 2,406	$ 9,968	$ 149
Income (loss) from discontinued operations, net of tax	0	0	(3)	(1)
Net income (loss)	3,104	2,406	9,965	148
Dividends and undistributed earnings allocated to participating securities	(26)	(20)	(84)	(5)
Preferred stock dividends	(79)	(67)	(200)	(212)
Issuance cost for redeemed preferred stock	(12)	0	(12)	(22)
Net income (loss) available to common stockholders	$ 2,987	$ 2,319	$ 9,669	$ (91)
Total weighted-average basic common shares outstanding	438.8	457.8	449.2	457.4
Effect of dilutive securities:
Stock options	0.6	0.4	0.7	0.0
Other contingently issuable shares	1.1	0.3	1.0	0.0
Total effect of dilutive securities	1.7	0.7	1.7	0.0
Total weighted-average diluted common shares outstanding	440.5	458.5	450.9	457.4
Basic earnings per common share:
Net income (loss) from continuing operations (in dollars per share)	$ 6.81	$ 5.07	$ 21.53	$ (0.20)
Income (loss) from discontinued operations	0.00	0.00	(0.01)	0.00
Net income (loss) per basic common share (in dollars per share)	6.81	5.07	21.52	(0.20)
Diluted earnings per common share:
Net income (loss) from continuing operations (in dollars per share)	6.78	5.06	21.45	(0.20)
Income (loss) from discontinued operations	0.00	0.00	(0.01)	0.00
Net income (loss) per diluted common share (in dollars per share)	$ 6.78	$ 5.06	$ 21.44	$ (0.20)