(Effect of Cash Flows Hedges on Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	8 Months Ended	9 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Sep. 30, 2016	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Derivative, Remaining Maturity					2 years
Successor
Derivative [Line Items]
Additions and revaluations of derivatives designated as cash flow hedges, after-tax	$ 0
Successor | Cash Flow Hedging
Derivative [Line Items]
Beginning balance, after-tax	0
Additions and revaluations of derivatives designated as cash flow hedges, after-tax	0
Clearance of hedge results to earnings, after-tax	0
Ending balance, after-tax	0	$ 0		$ 0	$ 0
Predecessor
Derivative [Line Items]
Additions and revaluations of derivatives designated as cash flow hedges, after-tax		1	$ (3)	5		$ 34
Predecessor | Cash Flow Hedging
Derivative [Line Items]
Beginning balance, after-tax	$ (3)	(4)	10	7	$ 7	(24)
Additions and revaluations of derivatives designated as cash flow hedges, after-tax		1	(2)	3		21
Clearance of hedge results to earnings, after-tax		0	0	(13)		11
Ending balance, after-tax		$ (3)	$ 8	$ (3)		$ 8