Earnings (Loss) 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
Earnings Per Share Table [Line Items]
Net income (loss) available to common stockholders	$ 164	$ 308	$ 893	$ 93
Basic weighted-average shares	1,215,434	1,213,912	1,215,113	1,213,512
Effect of dilutive securities:
Diluted weighted-average shares	1,217,979	1,215,335	1,217,558	1,214,757
Earnings (loss) per common share:
Basic	$ 0.14	$ 0.25	$ 0.74	$ 0.08
Diluted	$ 0.13	$ 0.25	$ 0.73	$ 0.08
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	2,539	1,423	2,437	1,241
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	6	0	8	4