Income Taxes Level 4 (Details) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
		Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2018	Jul. 02, 2019	Jul. 01, 2019	Dec. 31, 2017
Valuation Allowance [Line Items]
Valuation allowance		$ (122)		$ (217)	$ (525)	$ (98)	$ (98)	$ (498)
Income tax benefit	[1]	10	$ (201)	(14)	(31)
Operating Loss Carryforwards, Valuation Allowance				97			$ 1,053
Disallowed interest expense carryforward					283
Global Intangible low tax income		5			21
Income tax expense related to reorganization adjustments			40
Gain (loss) recognized between fair value and tax basis			50
Tax Benefit for Removal of Valuation Allowance			10
Changes in enacted tax laws and tax rates		$ 0	$ 0	$ 6	$ 0

[1] Excludes income tax expense of $1, $1, $21, and $9 for the year ended December 31, 2020, the Successor period July 2, 2019 through December 31, 2019, the Predecessor period January 1, 2019 through July 1, 2019, and the year ended December 31, 2018, respectively, related to the Held for Sale Business.