Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
(Loss) Income (Numerator):
Net income (loss)	$ 314	$ (6,165)
Weighted-average number of shares:
Weighted average shares outstanding for computing basic earnings per common share (in shares)	1,075,459	1,068,878
Incremental common shares attributable to dilutive securities:
Number of shares as adjusted for purposes of computing diluted (loss) earnings per common share (in shares)	1,081,754	1,068,878
Basic (loss) earnings per common share (in dollars per share)	$ 0.29	$ (5.77)
Diluted (loss) earnings per common share (in dollars per share)	$ 0.29	$ (5.77)
Convertible Debt Securities
Incremental common shares attributable to dilutive securities:
Number of shares of common stock excluded from the computation of diluted earnings per share (in shares)		3,300
Common Class A
(Loss) Income (Numerator):
Net income (loss)		$ (6,165)
Net income (loss) applicable to common stock for computing basic earnings per common share	$ 314	(6,165)
Net income (loss) as adjusted for purposes of computing diluted earnings per common share	$ 314	$ (6,165)
Weighted-average number of shares:
Outstanding during period (in shares)	1,092,970	1,083,588
Non-vested restricted stock (in shares)	(17,511)	(14,710)
Weighted average shares outstanding for computing basic earnings per common share (in shares)	1,075,459	1,068,878
Incremental common shares attributable to dilutive securities:
Shares issuable under convertible securities (in shares)	10	0
Shares issuable under incentive compensation plans (in shares)	6,285	0
Number of shares as adjusted for purposes of computing diluted (loss) earnings per common share (in shares)	1,081,754	1,068,878
Basic (loss) earnings per common share (in dollars per share)	$ 0.29	$ (5.77)
Diluted (loss) earnings per common share (in dollars per share)	$ 0.29	$ (5.77)
Number of shares of common stock excluded from the computation of diluted earnings per share (in shares)	2,700	5,400