Debt and Equity Transactions (Unaudited) Interest, Dividends and Maturities (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Capitalized Interest [Line Items]
Interest costs incurred	$ 210		$ 224
Dividends Payable, Date Declared	Mar. 24, 2015
Authorized Quarterly Rate Of Common Stock Dividend	$ 0.0500	$ 0.3125
Dividends Payable, Date to be Paid	May 01, 2015
Dividends Payable, Date of Record	Apr. 15, 2015
Property, Plant, Equipment and Mining Development Costs, Net [Member]
Capitalized Interest [Line Items]
Interest costs capitalized	45		40
Oil and Gas Properties Not Subject to Amortization [Member]
Capitalized Interest [Line Items]
Interest costs capitalized	$ 19		$ 23