Segment Information - Schedule of Revenue by Geographic Location (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
Revenue from geographic segments
Revenue	$ 3,394	$ 3,786	$ 3,968	$ 4,594	$ 6,635	$ 6,250	$ 5,935	$ 5,731	$ 15,742	$ 24,551	$ 22,364
UNITED STATES
Revenue from geographic segments
Revenue									5,800	11,499	10,133
Canada and other
Revenue from geographic segments
Revenue									839	1,336	1,446
North America
Revenue from geographic segments
Revenue									6,639	12,835	11,579
Latin America
Revenue from geographic segments
Revenue									1,847	2,300	2,368
Europe/Africa/Russia Caspian
Revenue from geographic segments
Revenue									3,555	4,705	4,359
Middle East/Asia Pacific
Revenue from geographic segments
Revenue									$ 3,701	$ 4,711	$ 4,058