Income Taxes Income Taxes - Gross Unrecognized Tax Benefits (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
Successor [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Beginning Balance	$ 709		$ 741
Decreases related to positions taken on items from prior years	(2)		(44)
Increases related to positions taken on items from prior years	9		74
Increases related to positions taken in the current year	28		9
Settlement of uncertain tax positions with tax authorities	1		(13)
Decreases due to expiration of statutes of limitations	(5)		(5)
Exchange (gain) loss	1		(13)
Unrecognized Tax Benefits, Ending Balance	741	$ 709	749
Total unrecognized tax benefits that, if recognized, would impact the effective tax rate	253		157
Total amount of interest and penalties (benefit) recognized in Provision for income taxes on continuing operations	1		11
Total accrual for interest and penalties associated with unrecognized tax benefits	47		$ 45
Predecessor [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Beginning Balance	$ 538	596		$ 906
Decreases related to positions taken on items from prior years		(19)		(46)
Increases related to positions taken on items from prior years		3		33
Increases related to positions taken in the current year		49		55
Settlement of uncertain tax positions with tax authorities		(6)		(314)
Decreases due to expiration of statutes of limitations		(86)		(41)
Exchange (gain) loss		1		3
Unrecognized Tax Benefits, Ending Balance		538		596
Total unrecognized tax benefits that, if recognized, would impact the effective tax rate		188		253
Total amount of interest and penalties (benefit) recognized in Provision for income taxes on continuing operations		(27)		10
Total accrual for interest and penalties associated with unrecognized tax benefits		$ 40		$ 98