Revenue Recognition (Schedule of Adoption of ASC 606) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Oil and gas	$ 1,266	$ 809
Oil and gas production	213	$ 141
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Oil and gas	1,266
Oil and gas production	213
ASC 605 (Without Adoption of ASC 606) | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Oil and gas	1,223
Oil and gas production	170
Effect of Change Higher (Lower) | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Oil and gas	43
Oil and gas production	$ 43