Business Segments (Schedule of Revenue and Long-Lived Assets, By Geographical Area) (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
Revenues from External Customers and Long-Lived Assets [Line Items]
Consolidated revenue	$ 5,322	$ 6,483	$ 5,589	$ 6,065	$ 5,559	$ 6,395	$ 5,708	$ 6,263	$ 23,459	$ 23,925	$ 22,756
Consolidated long-lived assets	89,564				83,167				89,564	83,167	81,362
U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Consolidated revenue									22,371	22,508	21,211
Consolidated long-lived assets	87,552				80,709				87,552	80,709	78,581
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Consolidated revenue									1,088	1,417	1,545
Consolidated long-lived assets	$ 2,012				$ 2,458				$ 2,012	$ 2,458	$ 2,781