Stockholders' Equity Tax Benefit (Expense) on Net Activity (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	8 Months Ended	9 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Sep. 30, 2018	Aug. 31, 2017	Sep. 30, 2018
Successor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)	$ 0		$ 0		$ (1)
Successor [Member] | Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)	0		1		2
Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)		$ (32)		$ (144)
Predecessor [Member] | Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)		0		6
Pension Plan | Successor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)	0		(1)		(3)
Pension Plan | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)		(31)		(145)
Other Benefit Plans | Successor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)	$ 0		$ 0		$ 0
Other Benefit Plans | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax Benefit (Expense)		$ (1)		$ (5)