Income Taxes Income Taxes - Operating Loss and Tax Credit Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Predecessor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		$ 1,523
Deferred Tax Assets, Tax Credit Carryforwards		285
Total Operating Loss and Tax Credit Carryforwards		1,808
Successor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 1,525
Deferred Tax Assets, Tax Credit Carryforwards	165
Total Operating Loss and Tax Credit Carryforwards	1,690
Expiring within Five Years [Member] | Predecessor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		41
Deferred Tax Assets, Tax Credit Carryforwards		10
Expiring within Five Years [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	42
Deferred Tax Assets, Tax Credit Carryforwards	10
Expiring After Five Years Or Having Indefinite Expiration [Member] | Predecessor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		1,482
Deferred Tax Assets, Tax Credit Carryforwards		$ 275
Expiring After Five Years Or Having Indefinite Expiration [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	1,483
Deferred Tax Assets, Tax Credit Carryforwards	$ 155