Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share Table [Line Items]
Net income (loss) available to common stockholders	$ 308	$ 220	$ 93	$ 724
Basic weighted-average shares	1,213,912	1,212,270	1,213,512	1,211,938
Effect of dilutive securities:
Diluted weighted-average shares	1,215,335	1,214,165	1,214,757	1,213,943
Earnings (loss) per common share:
Basic	$ 0.25	$ 0.18	$ 0.08	$ 0.60
Diluted	$ 0.25	$ 0.18	$ 0.08	$ 0.60
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,423	1,790	1,241	1,809
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0	105	4	196