Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of shares of common stock excluded from the computation of diluted earnings per share	3,200	3,200	6,800
Income (Loss) (Numerator)
Net income (loss)	$ 2,033	$ (1,232)	$ (5,269)
Net income (loss) applicable to common stock for computing basic earnings (loss) per common share	2,033	(1,232)	(5,269)
Net income (loss) as adjusted for purposes of computing diluted earnings (loss) per common share	$ 2,033	$ (1,232)	$ (5,269)
Weighted average number of shares:
Outstanding during period (in shares)	1,077,393	1,096,284	1,088,730
Non-vested restricted stock (in shares)	(17,852)	(17,154)	(17,289)
Weighted average shares outstanding for computing basic earnings (loss) per common share (in shares)	1,059,541	1,079,130	1,071,441
Incremental common shares attributable to dilutive securities:
Shares issuable under convertible securities (in shares)	10	0	0
Shares issuable under incentive compensation plans (in shares)	7,227	0	0
Number of shares as adjusted for purposes of computing diluted earnings (loss) per common share (in shares)	1,066,778	1,079,130	1,071,441
Basic earnings (loss) per common share (in dollars per share)	$ 1.92	$ (1.14)	$ (4.92)
Diluted earnings (loss) per common share (in dollars per share)	$ 1.91	$ (1.14)	$ (4.92)
Stock compensation plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of shares of common stock excluded from the computation of diluted earnings per share		5,300	3,000