CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	20,000,000	20,000,000
Preferred stock, shares outstanding (shares)	5,839,506	7,251,515
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,500,000,000	1,000,000,000
Common stock, shares issued	896,279,353	664,795,509
Treasury stock, common shares	1,220,504	1,437,724
VIE, cash and cash equivalents	$ 882	$ 825
VIE. proved natural gas and oil properties	66,451	63,843
VIE. accumulated depreciation, depletion and amortization	(62,726)	(59,365)
VIE. other current liabilities	1,798	2,219
Variable Interest Entities, Primary Beneficiary [Member]
VIE, cash and cash equivalents	1	1
VIE. proved natural gas and oil properties	488	488
VIE. accumulated depreciation, depletion and amortization	(458)	(428)
VIE. other current liabilities	$ 3	$ 8