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, 2016	Dec. 31, 2015
Successor [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Beginning Balance	$ 436
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(2)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	9
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	19
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	1
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(5)
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation	1
Unrecognized Tax Benefits, Ending Balance	459	$ 436
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	76
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	25
Predecessor [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Beginning Balance	$ 265	348	$ 558	$ 735
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions		(19)	(41)	(98)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions		3	32	13
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions		19	32	32
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities		(6)	(205)	(58)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		(81)	(30)	(30)
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation		1	2	(36)
Unrecognized Tax Benefits, Ending Balance		265	348	558
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		188	253	386
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		(27)	10	(14)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		$ 22	$ 71	$ 88