Debt and Equity Transactions (Unaudited) Interest, Dividends and Maturities (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Capitalized Interest [Line Items]
Interest costs incurred	$ 215	$ 225	$ 425	$ 449
Dividends Payable, Date Declared			Jun. 24, 2015
Dividends declared per share of common stock	$ 0.1605	$ 0.3125	$ 0.2105	$ 0.625
Authorized Quarterly Rate Of Common Stock Dividend	$ 0.0500
Dividends Payable, Date to be Paid	Aug. 03, 2015
Dividends Payable, Date of Record	Jul. 15, 2015
Special Dividend, Per Share	$ 0.1105
Property, Plant, Equipment and Mining Development Costs, Net [Member]
Capitalized Interest [Line Items]
Interest costs capitalized	$ 47	$ 39	$ 92	$ 79
Oil and Gas Properties Not Subject to Amortization [Member]
Capitalized Interest [Line Items]
Interest costs capitalized	$ 19	$ 22	$ 38	$ 45