Debt and Equity Transactions (Unaudited) Interest, Dividends and Maturities (Details) - USD ($) shares in Millions, $ in Millions			1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 29, 2016	Jan. 05, 2016	Aug. 04, 2016	Jul. 31, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jan. 05, 2016	Dec. 31, 2015
Capitalized Interest [Line Items]
Interest costs incurred					$ 218	$ 208	$ 436	$ 411
Stock Issued During Period, Shares, New Issues		4			17				210	206
Fees and Commissions		$ 20
Property, Plant, Equipment and Mining Development Costs, Net [Member]
Capitalized Interest [Line Items]
Interest costs capitalized					$ 22	47	42	92
Oil and Gas Properties Not Subject to Amortization [Member]
Capitalized Interest [Line Items]
Interest costs capitalized					$ 0	$ 19	$ 7	$ 38
Subsequent Event [Member]
Capitalized Interest [Line Items]
Common Stock, Value of Shares Authorized for Issue in Transaction	$ 12
Stock Issued During Period, Shares, New Issues			8	3
Proceeds from Issuance of Common Stock, Gross				$ 226