Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 5	$ 201
Accounts receivable, net	345	581
Other current assets	329	174
Total current assets	679	956
Intercompany receivables	0	0
Natural gas and oil properties, using the full cost method	25,250	24,180
Other	520	525
Less: Accumulated depreciation, depletion and amortization	(20,503)	(20,049)
Total property and equipment, net	5,267	4,656
Investments in subsidiaries (equity method)	0	0
Operating lease assets	159
Deferred tax assets	407	0
Other long-term assets	205	185
TOTAL ASSETS	6,717	5,797	$ 7,521
LIABILITIES AND EQUITY
Accounts payable	525	609
Current operating lease liabilities	34
Other current liabilities	289	237
Total current liabilities	848	846
Intercompany payables	0	0
Long-term debt	2,242	2,318
Long-term operating lease liabilities	119
Pension and other postretirement liabilities	43	46
Other long-term liabilities	219	225
Negative carrying amount of subsidiaries, net	0	0
Total long-term liabilities	2,623	2,589
Commitments and contingencies
Total equity	3,246	2,362	$ 1,979	$ 917
TOTAL LIABILITIES AND EQUITY	6,717	5,797
Reportable Legal Entities | Parent
ASSETS
Cash and cash equivalents	5	201
Accounts receivable, net	0	4
Other current assets	7	8
Total current assets	12	213
Intercompany receivables	7,922	7,932
Natural gas and oil properties, using the full cost method	0	0
Other	169	197
Less: Accumulated depreciation, depletion and amortization	(144)	(154)
Total property and equipment, net	25	43
Investments in subsidiaries (equity method)	0	0
Operating lease assets	80
Deferred tax assets	0
Other long-term assets	19	19
TOTAL ASSETS	8,058	8,207
LIABILITIES AND EQUITY
Accounts payable	79	113
Current operating lease liabilities	8
Other current liabilities	108	115
Total current liabilities	195	228
Intercompany payables	0	0
Long-term debt	2,242	2,318
Long-term operating lease liabilities	66
Pension and other postretirement liabilities	43	46
Other long-term liabilities	11	54
Negative carrying amount of subsidiaries, net	2,255	3,199
Total long-term liabilities	4,617	5,617
Total equity	3,246	2,362
TOTAL LIABILITIES AND EQUITY	8,058	8,207
Reportable Legal Entities | Guarantors
ASSETS
Cash and cash equivalents	0	0
Accounts receivable, net	345	577
Other current assets	322	166
Total current assets	667	743
Intercompany receivables	0	0
Natural gas and oil properties, using the full cost method	25,195	24,128
Other	322	301
Less: Accumulated depreciation, depletion and amortization	(20,300)	(19,840)
Total property and equipment, net	5,217	4,589
Investments in subsidiaries (equity method)	23	24
Operating lease assets	79
Deferred tax assets	407
Other long-term assets	186	166
TOTAL ASSETS	6,579	5,522
LIABILITIES AND EQUITY
Accounts payable	446	496
Current operating lease liabilities	26
Other current liabilities	181	122
Total current liabilities	653	618
Intercompany payables	7,920	7,932
Long-term debt	0	0
Long-term operating lease liabilities	53
Pension and other postretirement liabilities	0	0
Other long-term liabilities	208	171
Negative carrying amount of subsidiaries, net	0	0
Total long-term liabilities	261	171
Total equity	(2,255)	(3,199)
TOTAL LIABILITIES AND EQUITY	6,579	5,522
Reportable Legal Entities | Non-Guarantors
ASSETS
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Other current assets	0	0
Total current assets	0	0
Intercompany receivables	0	0
Natural gas and oil properties, using the full cost method	55	52
Other	29	27
Less: Accumulated depreciation, depletion and amortization	(59)	(55)
Total property and equipment, net	25	24
Investments in subsidiaries (equity method)	0	0
Operating lease assets	0
Deferred tax assets	0
Other long-term assets	0	0
TOTAL ASSETS	25	24
LIABILITIES AND EQUITY
Accounts payable	0	0
Current operating lease liabilities	0
Other current liabilities	0	0
Total current liabilities	0	0
Intercompany payables	2	0
Long-term debt	0	0
Long-term operating lease liabilities	0
Pension and other postretirement liabilities	0	0
Other long-term liabilities	0	0
Negative carrying amount of subsidiaries, net	0	0
Total long-term liabilities	0	0
Total equity	23	24
TOTAL LIABILITIES AND EQUITY	25	24
Eliminations
ASSETS
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Other current assets	0	0
Total current assets	0	0
Intercompany receivables	(7,922)	(7,932)
Natural gas and oil properties, using the full cost method	0	0
Other	0	0
Less: Accumulated depreciation, depletion and amortization	0	0
Total property and equipment, net	0	0
Investments in subsidiaries (equity method)	(23)	(24)
Operating lease assets	0
Deferred tax assets	0
Other long-term assets	0	0
TOTAL ASSETS	(7,945)	(7,956)
LIABILITIES AND EQUITY
Accounts payable	0	0
Current operating lease liabilities	0
Other current liabilities	0	0
Total current liabilities	0	0
Intercompany payables	(7,922)	(7,932)
Long-term debt	0	0
Long-term operating lease liabilities	0
Pension and other postretirement liabilities	0	0
Other long-term liabilities	0	0
Negative carrying amount of subsidiaries, net	(2,255)	(3,199)
Total long-term liabilities	(2,255)	(3,199)
Total equity	2,232	3,175
TOTAL LIABILITIES AND EQUITY	$ (7,945)	$ (7,956)