Chapter 11 Proceedings and Ability to continue as a Going Concern - Liabilities Subject to Compromise (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Liabilities Subject to Compromise	$ 7,634	$ 7,634	$ 0
Liabilities Subject To Compromise, Accrued Interest	207	207
Liabilities Subject to Compromise, Debt and Accrued Interest	7,634	7,634
Contractual interest expense on Notes in excess of recorded interest expense	(133)	133
Senior Notes | Senior Notes, 5.125% due 2020
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	365	365
Senior Notes | Exchangeable Senior Notes, 5.875 Percent due 2021
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	1,265	1,265
Senior Notes | Senior Notes, 7.75 Percent due 2021
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	750	750
Senior Notes | Senior Notes, 4.50% due 2022
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	646	646
Senior Notes | Senior Notes, 8.25 Percent due 2023
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	750	750
Senior Notes | Senior Notes, 9.875 Percent due 2024
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	790	790
Senior Notes | Senior Notes, 9.875 Percent due 2025
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	600	600
Senior Notes | Senior Notes, 6.50% due 2036
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	453	453
Senior Notes | Senior Notes, 6.80% due 2037
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	259	259
Senior Notes | Senior Notes, 7.00% due 2038
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	461	461
Senior Notes | Senior Notes, 9.875% due 2039
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	250	250
Senior Notes | Senior Notes, 6.75% due 2040
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	463	463
Senior Notes | Senior Notes, 5.95% due 2042
Debt Instrument [Line Items]
Liabilities Subject To Compromise, Debt	$ 375	$ 375