Financial Instruments Cash Flow Hedges Included in AOCI (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2017	Aug. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Remaining Maturity			2 years
Successor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Additions and revaluations of derivatives designated as cash flow hedges	$ 3		$ (24)
Predecessor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Additions and revaluations of derivatives designated as cash flow hedges		$ 5		$ 32
Scenario, Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
After-tax net loss to be reclassified from AOCL into earnings over the next twelve months			9
Cash Flow Hedging [Member] | Successor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash Flow Hedges Derivative Instruments at Fair Value, Beginning Balance	0		(2)
Additions and revaluations of derivatives designated as cash flow hedges	(2)		(19)
Clearance of hedge results to earnings	0		(5)
Cash Flow Hedges Derivative Instruments at Fair Value, Ending Balance	(2)	0	$ (26)
Cash Flow Hedging [Member] | Predecessor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash Flow Hedges Derivative Instruments at Fair Value, Beginning Balance	$ (3)	7		(24)
Additions and revaluations of derivatives designated as cash flow hedges		3		20
Clearance of hedge results to earnings		(13)		11
Cash Flow Hedges Derivative Instruments at Fair Value, Ending Balance		$ (3)		$ 7