Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended	9 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 338			$ (13)			$ 412	$ 224
Effective tax rate (as percent)	1127.00%			22.00%			3745.00%	533.00%
Federal statutory income tax rate (as percent)							12.50%
Change in valuation allowance on deferred tax asset		$ 43
Unrecognized tax benefits	$ 280						$ 280
Unrecognized tax benefits that would impact effective tax rate	105						105
Net accrued interest	9						9
Interest and penalty expense for accruals	1						$ 4
Change in valuation allowance			$ 100
Impairment charges on long-lived assets held-for-use		66
Income tax benefit associated with impairment charges of long-lived asset held-for-use		$ 2
Impairment charges on long-lived assets held-for-sale			$ 6	$ 52
Income tax benefit associated with impairment charges of long-lived asset held-for-sale				$ 15
Goodwill impairment charge					$ 299
Income tax benefit associated with goodwill impairment charges					$ 20
Foreign Tax Authority
Income Tax Contingency [Line Items]
Income tax expense from write-down of deferred tax assets	$ 48
Foreign Tax Authority | GAAS
Income Tax Contingency [Line Items]
Foreign income tax rate differential (as percent)			15.00%						25.00%
Income tax benefit on reduction of deferred tax liability									$ 7
Luxembourg Inland Revenue | Foreign Tax Authority
Income Tax Contingency [Line Items]
Effective tax rate (as percent)	24.90%					26.00%
Change in valuation allowance on deferred tax asset	$ 229
Income tax expense from write-down of deferred tax assets	10
Her Majesty's Revenue and Customs (HMRC) | Foreign Tax Authority
Income Tax Contingency [Line Items]
Change in valuation allowance on deferred tax asset	$ 25