Earnings Per Share (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ (29)	$ 51	$ 208	$ 77	$ 284	$ 351	$ 230	$ 712
Mandatory convertible preferred stock dividend				27				81
Participating securities - mandatory convertible preferred stock				7			1	83
Net Income (Loss) Attributable to Common Stock	$ (29)			$ 43			$ 229	$ 548
Number of common shares: Weighted average outstanding	581,171,753			499,812,926			577,912,421	496,458,435
Number of common shares: Effect of issuance of non-vested restricted common stock				1,202,585			640,365	883,512
Number of common shares: Effect of issuance of non-vested performance units				1,275,268			1,276,072	1,185,724
Number of common shares: Weighted average and potential dilutive outstanding	581,171,753			502,290,779			579,828,858	498,527,671
Earnings (loss) per common share: Basic	$ (0.05)			$ 0.09			$ 0.40	$ 1.11
Earnings (loss) per common share: Diluted	$ (0.05)			$ 0.09			$ 0.39	$ 1.10