Investments In and Advances To Affiliates - Summarized Financial Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Revenue									$ 14,963	$ 17,146	$ 15,891
Operating margin	$ 718	$ 673	$ 754	$ 721	$ 708	$ 767	$ 819	$ 794	2,866	3,088	3,247
Net income	41	$ 203	$ 264	$ 254	298	$ 508	$ 275	$ 66	762	1,147	551
Assets, Current	6,866				7,826				6,866	7,826
Liabilities, Current	6,950				6,997				6,950	6,997
Liabilities, Noncurrent	23,191				24,566				23,191	24,566
Stockholders' Equity Attributable to Noncontrolling Interest	3,022				3,053				3,022	3,053
Stockholders' Equity Attributable to Parent	3,149				4,272				3,149	4,272
Undistributed Earnings Of Minority Owned Affiliates Included In Retained Earnings	244								244
Distributions Received From Minority Owned Affiliates									18	28	6
Basis Difference Between Carrying Amount And Investment	162								162
Minority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue									641	928	1,099
Operating margin									152	206	295
Net income									210	59	53
Assets, Current	376				450				376	450
Assets, Noncurrent	2,132				1,748				2,132	1,748
Liabilities, Current	435				299				435	299
Liabilities, Noncurrent	1,044				935				1,044	935
Stockholders' Equity Attributable to Noncontrolling Interest	0				17				0	17
Stockholders' Equity Attributable to Parent	1,029				947				1,029	947
Majority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue									24	2	2
Operating margin									11	0	0
Net income									6	0	$ 0
Assets, Current	20				0				20	0
Assets, Noncurrent	211				15				211	15
Liabilities, Current	21				0				21	0
Liabilities, Noncurrent	153				67				153	67
Stockholders' Equity Attributable to Noncontrolling Interest	0				0				0	0
Stockholders' Equity Attributable to Parent	$ 57				$ (52)				$ 57	$ (52)