Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Activity for equity attributable to noncontrolling interests
Balance at January 1	$ 146,722	$ 153,886
Net Income (Loss)	9,269	(431)	$ 4,710
Balance at December 31	149,319	146,722	153,886
Noncontrolling Interests
Activity for equity attributable to noncontrolling interests
Balance at January 1	1,166	1,170	1,163
Net Income (Loss)	74	66	123
Distributions to noncontrolling interests	(78)	(63)	(128)
Other changes, net	33	(7)	12
Balance at December 31	$ 1,195	$ 1,166	$ 1,170