Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share Table [Line Items]
Net income (loss) available to common stockholders	$ 220	$ 129	$ 724	$ 416
Basic weighted-average shares	1,212,270	1,023,587	1,211,938	893,706
Effect of dilutive securities:
Diluted weighted-average shares	1,214,165	1,026,504	1,213,943	896,322
Earnings (loss) per common share:
Basic	$ 0.18	$ 0.13	$ 0.60	$ 0.47
Diluted	$ 0.18	$ 0.13	$ 0.60	$ 0.46
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,790	2,387	1,809	2,102
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	105	530	196	514