Stockholders' Equity Stockholders' Equity (Narrative) (Details) - USD ($) $ in Millions		8 Months Ended	12 Months Ended
	Aug. 30, 2017	Aug. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Class of Stock [Line Items]
Treasury Stock, Shares				0	0
Predecessor [Member]
Class of Stock [Line Items]
Treasury Stock, Shares	87,000,000	0	87,041,000			87,041,000
Excess of Cost of Treasury Stock over Par Value		$ 0	$ 0
Tax benefit recorded in Stockholders' Equity			33
Tax benefits			21
Successor [Member]
Class of Stock [Line Items]
Treasury Stock, Shares		0
Retained Earnings [Member] | Predecessor [Member]
Class of Stock [Line Items]
Excess of Cost of Treasury Stock over Par Value	$ 5,657	$ 5,657	758
Additional Paid-in Capital [Member] | Predecessor [Member]
Class of Stock [Line Items]
Excess of Cost of Treasury Stock over Par Value	$ 1,044	$ 1,044	$ 154