Subsequent Events Subsequent Events - Narrative (Details) MMcf in Millions, $ in Millions						1 Months Ended	12 Months Ended
	Feb. 20, 2017 USD ($)	Feb. 15, 2017 USD ($) a well MMcf	Jan. 19, 2017 shares	Jan. 13, 2017 USD ($) a well MMcf	Jan. 06, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 20, 2017 USD ($)
Subsequent Event [Line Items]
Cash paid to purchase debt							$ 2,734	$ 508	$ 3,362
Proceeds from divestitures of proved and unproved properties							1,406	189	5,813
Gas Gathering, Transportation, Marketing and Processing Costs							$ 4,778	$ 7,130	$ 12,236
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage							5.00%
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares							1,012,032
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Conversion of Stock, Shares Converted | shares							134,000
Preferred Stock, Dividend Rate, Percentage							5.00%
5.75% Cumulative Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage							5.75%
5.75% Cumulative Convertible Preferred Stock [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares							59,141,429
5.75% Cumulative Convertible Preferred Stock [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Conversion of Stock, Shares Converted | shares							653,872
Preferred Stock, Dividend Rate, Percentage							5.75%
5.75% Cumulative Convertible Preferred Stock Series A [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage							5.75%
5.75% Cumulative Convertible Preferred Stock Series A [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares							60,032,734
5.75% Cumulative Convertible Preferred Stock Series A [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Conversion of Stock, Shares Converted | shares							624,137
Preferred Stock, Dividend Rate, Percentage							5.75%
Senior Notes [Member]
Subsequent Event [Line Items]
Debt Instrument, Repurchased Face Amount							$ 325
Cash paid to purchase debt							$ 300
Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Repurchased Face Amount						$ 221
Cash paid to purchase debt					$ 286	$ 224
Gas Gathering, Transportation, Marketing and Processing Costs	$ 290
Purchase Commitment, Remaining Minimum Amount Committed	450
Subsequent Event [Member] | Natural Gas [Member]
Subsequent Event [Line Items]
Purchase Commitment, Remaining Minimum Amount Committed	110
Loss on Contract Termination	$ 100
Subsequent Event [Member] | Haynesville Shale [Member]
Subsequent Event [Line Items]
Proceeds from divestitures of proved and unproved properties		$ 465		$ 450
Number Of Net Acres | a		41,500		78,000
Productive Gas Wells, Number of Wells, Net | well				250
Wells | well		326
Subsequent Event [Member] | Haynesville Shale [Member] | Natural Gas [Member]
Subsequent Event [Line Items]
Proved Developed Reserves (Volume) | MMcf		50		30
Subsequent Event [Member] | Contingent Convertible Debt [Member]
Subsequent Event [Line Items]
Debt Instrument, Repurchased Face Amount					287
Subsequent Event [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Conversion of Stock, Shares Converted | shares			10,000,000
Subsequent Event [Member] | 5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.00%
Subsequent Event [Member] | 5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares			150,948
Subsequent Event [Member] | 5.75% Cumulative Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.75%
Subsequent Event [Member] | 5.75% Cumulative Convertible Preferred Stock [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares			72,600
Subsequent Event [Member] | 5.75% Cumulative Convertible Preferred Stock Series A [Member]
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.75%
Subsequent Event [Member] | 5.75% Cumulative Convertible Preferred Stock Series A [Member] | Preferred Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares			12,500
Subsequent Event [Member] | 6.5% Senior Notes Due 2017 [Member]
Subsequent Event [Line Items]
Debt Instrument, Repurchased Face Amount										$ 133
Debt Instrument, Interest Rate, Stated Percentage										6.50%
Subsequent Event [Member] | Senior Notes [Member]
Subsequent Event [Line Items]
Debt Instrument, Repurchased Face Amount					$ 2