Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Financial Assets
Commodity derivatives, assets	$ 220	$ 269
Financial Liabilities
Commodity derivatives, liability	188	192
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Financial Assets
Deferred compensation investments	21	297
Commodity derivatives, assets	228	297
Loans to related parties - project financing	808	913
Financial Liabilities
Total debt, excluding capital leases, carrying amount	24,062	21,707
Commodity derivatives, liability	199	214
Deferred Compensation Liquidation [Member]
Financial Assets
Deferred compensation investments	267
Portion at Fair Value, Fair Value Disclosure [Member]
Financial Assets
Deferred compensation investments	21	297
Commodity derivatives, assets	228	297
Loans to related parties - project financing	808	913
Financial Liabilities
Total debt, excluding capital leases, fair value	24,785	25,191
Commodity derivatives, liability	$ 199	$ 214