Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
(Loss) Income (Numerator):
Net income	$ 544	$ 366	$ 1,525	$ 1,057
Net income applicable to common stock for computing basic earnings per common share	544	366	1,525	1,057
Net income as adjusted for purposes of computing diluted earnings per common share	$ 544	$ 366	$ 1,525	$ 1,057
Weighted-average number of shares:
Outstanding during period (in shares)	1,079,917	1,097,496	1,095,223	1,096,017
Non-vested restricted stock (in shares)	(17,833)	(16,991)	(18,117)	(17,345)
Weighted average shares outstanding for computing basic earnings per common share (in shares)	1,062,084	1,080,505	1,077,106	1,078,672
Incremental common shares attributable to dilutive securities:
Shares issuable under convertible securities (in shares)	10	10	10	10
Shares issuable under incentive compensation plans (in shares)	7,063	5,151	6,763	4,686
Number of shares as adjusted for purposes of computing diluted earnings (loss) per common share (in shares)	1,069,157	1,085,666	1,083,879	1,083,368
Basic earnings per common share (in dollars per share)	$ 0.51	$ 0.34	$ 1.42	$ 0.98
Diluted earnings per common share (in dollars per share)	$ 0.51	$ 0.34	$ 1.41	$ 0.98
Number of shares of common stock excluded from the computation of diluted earnings per share (less than) (in shares)	3,900	400	3,000	4,000