Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share Table [Line Items]
Net income (loss) available to common stockholders	$ 304	$ 303	$ 729	$ (215)
Basic weighted-average shares	1,215,250	1,213,601	1,214,950	1,213,310
Effect of dilutive securities:
Diluted weighted-average shares (1)	1,217,476	1,214,581	1,217,344	1,213,310	[1]
Earnings (loss) per common share:
Basic	$ 0.25	$ 0.25	$ 0.60	$ (0.18)
Diluted	$ 0.25	$ 0.25	$ 0.60	$ (0.18)
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	2,208	980	2,385	0
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	18	0	9	0
Nonvested restricted stock units [Member]
Earnings (loss) per common share:
Number of weighted-average shares excluded from computation of diluted earnings per common share				1,100

[1] For the six months ended June 30, 2020, 1.1 million weighted-average nonvested restricted stock units have been excluded from the computation of diluted earnings (loss) per common share as their inclusion would be antidilutive due to our loss available to common stockholders.