CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Dividends payable on common and preferred stock	$ 101	$ 99	$ 90
Natural gas and oil properties adjusted as a result of an increase in accrued acquisition, drilling and completion costs	(75)	176	161
Other property and equipment adjusted as a result of an increase in accrued costs	(25)	64	(19)
Liabilities related to the purchase of proved and unproved properties	$ 242	$ 81	$ 371