Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share Table [Line Items]
Net income (loss) available to common stockholders		$ 303	$ 310	$ (215)	$ 504
Basic weighted-average shares		1,213,601	1,212,045	1,213,310	1,211,769
Effect of dilutive securities:
Diluted weighted-average shares (1)	[1]	1,214,581	1,214,065	1,213,310	1,213,830
Earnings (loss) per common share:
Basic		$ 0.25	$ 0.26	$ (0.18)	$ 0.42
Diluted		$ 0.25	$ 0.26	$ (0.18)	$ 0.41
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements		980	1,792	0	1,818
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements		0	228	0	243
Nonvested restricted stock units [Member]
Earnings Loss Per Common Share from Continuing Operations Textuals [Abstract]
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.